diff --git a/docs/SPECIFICATION.md b/docs/SPECIFICATION.md
index b975538..a8a57f5 100644
--- a/docs/SPECIFICATION.md
+++ b/docs/SPECIFICATION.md
@@ -232,7 +232,18 @@ REST API認証用のAPIキーを管理するモデル。
 |------------|----------|
 | Telegram | config.iniでBot Token設定、プロフィールでChat ID入力 |
 
-### 4.5 プロフィール機能
+### 4.5 CSVエクスポート機能
+
+| 機能 | 説明 |
+|------|------|
+| CSVダウンロード | 統計ページから課題一覧をCSVファイルとしてダウンロード (`GET /assignments/export`) |
+| 期間フィルタ | 提出期限（`due_date`）を基準に開始日・終了日で絞り込み可能 |
+| 科目フィルタ | 特定の科目のみを対象にエクスポート可能 |
+| 全件エクスポート | 期間・科目を未指定の場合は全課題を出力 |
+| CSVカラム | ID, タイトル, 科目, 説明, 重要度, 提出期限, 完了状態, 完了日時, 登録日時 |
+| エンコーディング | UTF-8 BOM付き（Excel直接開き対応） |
+
+### 4.6 プロフィール機能
 
 | 機能 | 説明 |
 |------|------|
diff --git a/internal/database/database.go b/internal/database/database.go
index 05f83a3..df80c9d 100644
--- a/internal/database/database.go
+++ b/internal/database/database.go
@@ -76,13 +76,19 @@ func Connect(dbConfig config.DatabaseConfig, debug bool) error {
 }
 
 func Migrate() error {
-	return DB.AutoMigrate(
+	if err := DB.AutoMigrate(
 		&models.User{},
 		&models.Assignment{},
 		&models.RecurringAssignment{},
 		&models.APIKey{},
 		&models.UserNotificationSettings{},
-	)
+	); err != nil {
+		return err
+	}
+
+	return DB.Model(&models.RecurringAssignment{}).
+		Where("recurrence_type = ? AND generation_lead_days = 0", models.RecurrenceWeekly).
+		Update("generation_lead_days", 7).Error
 }
 
 func GetDB() *gorm.DB {
diff --git a/internal/handler/assignment_handler.go b/internal/handler/assignment_handler.go
index e5f865e..dd2ad4c 100644
--- a/internal/handler/assignment_handler.go
+++ b/internal/handler/assignment_handler.go
@@ -1,6 +1,7 @@
 package handler
 
 import (
+	"encoding/csv"
 	"net/http"
 	"strconv"
 	"strings"
@@ -108,6 +109,8 @@ func (h *AssignmentHandler) New(c *gin.Context) {
 	role, _ := c.Get(middleware.UserRoleKey)
 	name, _ := c.Get(middleware.UserNameKey)
 	now := time.Now()
+	tomorrow := now.AddDate(0, 0, 1)
+	defaultDue := time.Date(tomorrow.Year(), tomorrow.Month(), tomorrow.Day(), 23, 59, 0, 0, now.Location())
 
 	RenderHTML(c, http.StatusOK, "assignments/new.html", gin.H{
 		"title":          "課題登録",
@@ -115,6 +118,7 @@ func (h *AssignmentHandler) New(c *gin.Context) {
 		"userName":       name,
 		"currentWeekday": int(now.Weekday()),
 		"currentDay":     now.Day(),
+		"defaultDueDate": defaultDue.Format("2006-01-02T15:04"),
 	})
 }
 
@@ -217,6 +221,12 @@ func (h *AssignmentHandler) Create(c *gin.Context) {
 
 		dueTime := dueDate.Format("15:04")
 
+		generationLeadDays := 0
+		if v, err := strconv.Atoi(c.PostForm("generation_lead_days")); err == nil && v >= 0 {
+			generationLeadDays = v
+		}
+		generationLeadTime := c.PostForm("generation_lead_time")
+
 		recurringService := service.NewRecurringAssignmentService()
 		input := service.CreateRecurringAssignmentInput{
 			Title:                 title,
@@ -233,6 +243,8 @@ func (h *AssignmentHandler) Create(c *gin.Context) {
 			EndDate:               endDate,
 			ReminderEnabled:       reminderEnabled,
 			UrgentReminderEnabled: urgentReminderEnabled,
+			GenerationLeadDays:    generationLeadDays,
+			GenerationLeadTime:    generationLeadTime,
 			FirstDueDate:          dueDate,
 		}
 
@@ -353,7 +365,10 @@ func (h *AssignmentHandler) Toggle(c *gin.Context) {
 	userID := h.getUserID(c)
 	id, _ := strconv.ParseUint(c.Param("id"), 10, 32)
 
-	h.assignmentService.ToggleComplete(userID, uint(id))
+	assignment, err := h.assignmentService.ToggleComplete(userID, uint(id))
+	if err == nil && assignment.IsCompleted && assignment.RecurringAssignmentID != nil {
+		h.recurringService.TriggerForRecurring(*assignment.RecurringAssignmentID)
+	}
 
 	referer := c.Request.Referer()
 	if referer == "" {
@@ -459,6 +474,69 @@ func (h *AssignmentHandler) UnarchiveSubject(c *gin.Context) {
 	c.Redirect(http.StatusFound, "/statistics?include_archived=true")
 }
 
+func (h *AssignmentHandler) ExportCSV(c *gin.Context) {
+	userID := h.getUserID(c)
+
+	var from, to *time.Time
+	if fromStr := c.Query("from"); fromStr != "" {
+		if t, err := time.ParseInLocation("2006-01-02", fromStr, time.Local); err == nil {
+			from = &t
+		}
+	}
+	if toStr := c.Query("to"); toStr != "" {
+		if t, err := time.ParseInLocation("2006-01-02", toStr, time.Local); err == nil {
+			to = &t
+		}
+	}
+	subject := c.Query("subject")
+
+	assignments, err := h.assignmentService.GetForExport(userID, from, to, subject)
+	if err != nil {
+		c.String(http.StatusInternalServerError, "エクスポートに失敗しました")
+		return
+	}
+
+	filename := "assignments_" + time.Now().Format("20060102") + ".csv"
+	c.Header("Content-Type", "text/csv; charset=utf-8")
+	c.Header("Content-Disposition", "attachment; filename=\""+filename+"\"")
+
+	w := csv.NewWriter(c.Writer)
+	// UTF-8 BOM for Excel compatibility
+	c.Writer.Write([]byte("\xef\xbb\xbf"))
+
+	headers := []string{"ID", "タイトル", "科目", "説明", "重要度", "提出期限", "完了", "完了日時", "登録日時"}
+	w.Write(headers)
+
+	priorityLabel := map[string]string{"low": "低", "medium": "中", "high": "高"}
+	for _, a := range assignments {
+		completed := "未完了"
+		if a.IsCompleted {
+			completed = "完了"
+		}
+		completedAt := ""
+		if a.CompletedAt != nil {
+			completedAt = a.CompletedAt.Format("2006/01/02 15:04")
+		}
+		label := priorityLabel[a.Priority]
+		if label == "" {
+			label = a.Priority
+		}
+		w.Write([]string{
+			strconv.FormatUint(uint64(a.ID), 10),
+			a.Title,
+			a.Subject,
+			a.Description,
+			label,
+			a.DueDate.Format("2006/01/02 15:04"),
+			completed,
+			completedAt,
+			a.CreatedAt.Format("2006/01/02 15:04"),
+		})
+	}
+
+	w.Flush()
+}
+
 func (h *AssignmentHandler) StopRecurring(c *gin.Context) {
 	userID := h.getUserID(c)
 	id, err := strconv.ParseUint(c.Param("id"), 10, 32)
@@ -580,6 +658,12 @@ func (h *AssignmentHandler) UpdateRecurring(c *gin.Context) {
 		}
 	}
 
+	generationLeadDays := 0
+	if v, err := strconv.Atoi(c.PostForm("generation_lead_days")); err == nil && v >= 0 {
+		generationLeadDays = v
+	}
+	generationLeadTime := c.PostForm("generation_lead_time")
+
 	input := service.UpdateRecurringInput{
 		Title:              &title,
 		Description:        &description,
@@ -594,6 +678,8 @@ func (h *AssignmentHandler) UpdateRecurring(c *gin.Context) {
 		EndCount:           endCount,
 		EndDate:            endDate,
 		EditBehavior:       editBehavior,
+		GenerationLeadDays: &generationLeadDays,
+		GenerationLeadTime: &generationLeadTime,
 	}
 
 	_, err = h.recurringService.Update(userID, uint(id), input)
diff --git a/internal/repository/assignment_repository.go b/internal/repository/assignment_repository.go
index 51e0beb..5b77f3c 100644
--- a/internal/repository/assignment_repository.go
+++ b/internal/repository/assignment_repository.go
@@ -21,6 +21,15 @@ func (r *AssignmentRepository) Create(assignment *models.Assignment) error {
 	return r.db.Create(assignment).Error
 }
 
+func (r *AssignmentRepository) FindByRecurringAndDue(recurringID uint, dueDate time.Time) (*models.Assignment, error) {
+	var a models.Assignment
+	err := r.db.Where("recurring_assignment_id = ? AND due_date = ?", recurringID, dueDate).First(&a).Error
+	if err == gorm.ErrRecordNotFound {
+		return nil, nil
+	}
+	return &a, err
+}
+
 func (r *AssignmentRepository) FindByID(id uint) (*models.Assignment, error) {
 	var assignment models.Assignment
 	err := r.db.First(&assignment, id).Error
@@ -336,6 +345,22 @@ func (r *AssignmentRepository) GetArchivedSubjects(userID uint) ([]string, error
 	return subjects, err
 }
 
+func (r *AssignmentRepository) FindForExport(userID uint, from, to *time.Time, subject string) ([]models.Assignment, error) {
+	var assignments []models.Assignment
+	q := r.db.Where("user_id = ?", userID)
+	if from != nil {
+		q = q.Where("due_date >= ?", *from)
+	}
+	if to != nil {
+		q = q.Where("due_date < ?", to.AddDate(0, 0, 1))
+	}
+	if subject != "" {
+		q = q.Where("subject = ?", subject)
+	}
+	err := q.Order("due_date ASC").Find(&assignments).Error
+	return assignments, err
+}
+
 func (r *AssignmentRepository) GetSubjectsByUserIDWithArchived(userID uint, includeArchived bool) ([]string, error) {
 	var subjects []string
 	query := r.db.Model(&models.Assignment{}).
diff --git a/internal/router/router.go b/internal/router/router.go
index 7dac7c4..dd8f249 100644
--- a/internal/router/router.go
+++ b/internal/router/router.go
@@ -248,6 +248,7 @@ func Setup(cfg *config.Config) *gin.Engine {
 		auth.POST("/assignments/:id/toggle", assignmentHandler.Toggle)
 		auth.POST("/assignments/:id/delete", assignmentHandler.Delete)
 
+		auth.GET("/assignments/export", assignmentHandler.ExportCSV)
 		auth.GET("/statistics", assignmentHandler.Statistics)
 		auth.POST("/statistics/archive-subject", assignmentHandler.ArchiveSubject)
 		auth.POST("/statistics/unarchive-subject", assignmentHandler.UnarchiveSubject)
diff --git a/internal/service/assignment_service.go b/internal/service/assignment_service.go
index 65b02c2..7f86424 100644
--- a/internal/service/assignment_service.go
+++ b/internal/service/assignment_service.go
@@ -378,6 +378,10 @@ func (s *AssignmentService) GetStatistics(userID uint, filter StatisticsFilter)
 	return summary, nil
 }
 
+func (s *AssignmentService) GetForExport(userID uint, from, to *time.Time, subject string) ([]models.Assignment, error) {
+	return s.assignmentRepo.FindForExport(userID, from, to, subject)
+}
+
 func (s *AssignmentService) ArchiveSubject(userID uint, subject string) error {
 	return s.assignmentRepo.ArchiveBySubject(userID, subject)
 }
diff --git a/internal/service/recurring_assignment_service.go b/internal/service/recurring_assignment_service.go
index 7d9d5f7..4d9556e 100644
--- a/internal/service/recurring_assignment_service.go
+++ b/internal/service/recurring_assignment_service.go
@@ -413,11 +413,6 @@ func (s *RecurringAssignmentService) generateNextIfPending(recurring *models.Rec
 		return nil
 	}
 
-	pendingCount, err := s.recurringRepo.CountPendingByRecurringID(recurring.ID)
-	if err != nil || pendingCount > 0 {
-		return err
-	}
-
 	latest, err := s.recurringRepo.GetLatestAssignmentByRecurringID(recurring.ID)
 	if err != nil {
 		return err
@@ -426,6 +421,10 @@ func (s *RecurringAssignmentService) generateNextIfPending(recurring *models.Rec
 		return nil
 	}
 
+	if !latest.IsCompleted && !latest.IsOverdue() {
+		return nil
+	}
+
 	nextDueDate := recurring.CalculateNextDueDate(latest.DueDate)
 
 	if recurring.GenerationLeadDays > 0 {
diff --git a/web/static/css/style.css b/web/static/css/style.css
index 922a645..d44cef6 100644
--- a/web/static/css/style.css
+++ b/web/static/css/style.css
@@ -1,5 +1,3 @@
-/* Custom styles for Homework Manager */
-
 :root {
     --primary-color: #4361ee;
     --secondary-color: #3f37c9;
@@ -13,8 +11,8 @@ body {
     display: flex;
     flex-direction: column;
     background-color: #f8f9fa;
-    margin-top: 0 !important;
-    padding-top: 0 !important;
+    margin-top: 0;
+    padding-top: 0;
 }
 
 .countdown {
@@ -27,7 +25,6 @@ main {
     flex: 1;
 }
 
-/* Card enhancements */
 .card {
     border: none;
     border-radius: 0.75rem;
@@ -44,7 +41,6 @@ main {
     font-weight: 600;
 }
 
-/* Navbar customization */
 .navbar {
     box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
 }
@@ -53,7 +49,6 @@ main {
     font-weight: 700;
 }
 
-/* Table improvements */
 .table {
     background-color: #fff;
     border-radius: 0.5rem;
@@ -69,7 +64,6 @@ main {
     background-color: rgba(67, 97, 238, 0.05);
 }
 
-/* Button styles */
 .btn {
     border-radius: 0.5rem;
     font-weight: 500;
@@ -85,25 +79,21 @@ main {
     border-color: var(--secondary-color);
 }
 
-/* Badge styles */
 .badge {
     font-weight: 500;
     padding: 0.4em 0.8em;
 }
 
-/* Form styles */
 .form-control:focus {
     border-color: var(--primary-color);
     box-shadow: 0 0 0 0.25rem rgba(67, 97, 238, 0.25);
 }
 
-/* Alert enhancements */
 .alert {
     border: none;
     border-radius: 0.5rem;
 }
 
-/* Stats cards */
 .card.bg-primary,
 .card.bg-warning,
 .card.bg-info,
@@ -119,27 +109,38 @@ main {
     box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
 }
 
-/* Tabs - Removed conflicted specific styles as they are managed in templates */
 .nav-tabs .nav-link {
     font-weight: 500;
+    font-size: 0.9rem;
+    padding: 0.5rem 1rem;
+    color: #6c757d;
+    border: none;
+}
+
+.nav-tabs .nav-link:hover {
+    color: #000;
+    border: none;
+}
+
+.nav-tabs .nav-link.active {
+    color: #000;
+    font-weight: 700;
+    border-bottom: 3px solid #000;
+    background: transparent;
 }
 
-/* Footer */
 .footer {
     border-top: 1px solid #e9ecef;
 }
 
-/* Login/Register cards */
 .card.shadow {
     border-radius: 1rem;
 }
 
-/* Empty states */
 .text-muted.display-1 {
-    color: #dee2e6 !important;
+    color: #dee2e6;
 }
 
-/* Responsive adjustments */
 @media (max-width: 768px) {
     .card-body {
         padding: 0.75rem;
@@ -150,68 +151,12 @@ main {
     }
 }
 
-.table td,
-.table th {
-    padding: 0.35rem 0.5rem !important;
-}
-
-.page-header {
-    margin-bottom: 0.75rem !important;
-}
-
-/* Animations for Anxiety/Urgency */
-@keyframes pulse-bg {
-
-    0%,
-    100% {
-        background-color: #fff3cd;
-    }
-
-    50% {
-        background-color: #ffe69c;
-    }
-}
-
-@keyframes pulse-bg-danger {
-
-    0%,
-    100% {
-        background-color: #f8d7da;
-    }
-
-    50% {
-        background-color: #f5c2c7;
-    }
-}
-
-@keyframes blink-text {
-
-    0%,
-    100% {
-        opacity: 1;
-    }
-
-    50% {
-        opacity: 0.7;
-    }
-}
-
-.anxiety-warning {
-    animation: pulse-bg 2s infinite;
-}
-
-.anxiety-danger {
-    animation: pulse-bg-danger 1s infinite;
-}
-
-/* Custom Table Styles - Compact */
 .custom-table thead th {
     border-bottom: 2px solid #dee2e6;
     font-size: 0.8rem;
     color: #495057;
     font-weight: 600;
-    padding-top: 0.5rem !important;
-    padding-bottom: 0.5rem !important;
+    padding: 0.35rem 0.5rem;
     white-space: nowrap;
 }
 
@@ -222,8 +167,7 @@ main {
 .custom-table tbody td {
     border-bottom: 1px solid #dee2e6;
     vertical-align: middle;
-    padding-top: 0.5rem !important;
-    padding-bottom: 0.5rem !important;
+    padding: 0.35rem 0.5rem;
     font-size: 0.9rem;
 }
 
@@ -231,7 +175,10 @@ main {
     border-bottom: none;
 }
 
-/* Compact form elements */
+.page-header {
+    margin-bottom: 0.75rem;
+}
+
 .form-control-custom,
 .form-select-custom,
 .btn-custom {
@@ -240,41 +187,87 @@ main {
     border-radius: 0.25rem;
 }
 
-/* Custom Tab Styles */
-.nav-tabs .nav-link {
-    font-size: 0.9rem;
-    padding: 0.5rem 1rem;
-    color: #6c757d;
-    /* text-muted */
-    border: none;
-}
-
-.nav-tabs .nav-link:hover {
-    color: #000;
-    border: none;
-}
-
-.nav-tabs .nav-link.active {
-    color: #000 !important;
-    font-weight: 700;
-    border-bottom: 3px solid #000 !important;
-    background: transparent;
-}
-
-/* Status Icon Size */
 .bi-circle,
 .bi-check-circle-fill {
     font-size: 1rem;
 }
 
-/* Urgency styles for countdown */
 .countdown-urgent {
     color: #dc3545;
     font-weight: 700;
-    animation: blink-text 1s infinite;
 }
 
 .countdown-warning {
     color: #fd7e14;
     font-weight: 700;
-}
\ No newline at end of file
+}
+
+@keyframes pulse-bg {
+    0%, 100% { background-color: #fff3cd; }
+    50%       { background-color: #ffe69c; }
+}
+
+@keyframes pulse-bg-danger {
+    0%, 100% { background-color: #f8d7da; }
+    50%       { background-color: #f5c2c7; }
+}
+
+@keyframes blink-text {
+    0%, 100% { opacity: 1; }
+    50%       { opacity: 0.7; }
+}
+
+@keyframes blink-banner {
+    0%, 100% { opacity: 1; }
+    50%       { opacity: 0.75; }
+}
+
+.anxiety-warning {
+    animation: pulse-bg 2s infinite;
+}
+
+.anxiety-danger {
+    animation: pulse-bg-danger 1s infinite;
+}
+
+.urgent-banner {
+    position: relative;
+    animation: blink-banner 1.5s infinite;
+}
+
+@media (prefers-reduced-motion: reduce) {
+    *, ::before, ::after {
+        animation-duration: 0.01ms !important;
+        animation-iteration-count: 1 !important;
+        transition-duration: 0.01ms !important;
+    }
+}
+
+#weekday_group,
+#day_group {
+    display: none;
+}
+
+.btn-touch {
+    min-width: 44px;
+    min-height: 44px;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+}
+
+.copy-feedback {
+    position: fixed;
+    bottom: 1.5rem;
+    right: 1.5rem;
+    z-index: 9999;
+    opacity: 0;
+    transform: translateY(0.5rem);
+    transition: opacity 0.2s ease, transform 0.2s ease;
+    pointer-events: none;
+}
+
+.copy-feedback.show {
+    opacity: 1;
+    transform: translateY(0);
+}
diff --git a/web/static/js/app.js b/web/static/js/app.js
index 69f9eba..136ce6a 100644
--- a/web/static/js/app.js
+++ b/web/static/js/app.js
@@ -7,9 +7,7 @@ const XSS = {
     },
 
     setTextSafe: function (element, text) {
-        if (element) {
-            element.textContent = text;
-        }
+        if (element) element.textContent = text;
     },
 
     sanitizeUrl: function (url) {
@@ -17,13 +15,9 @@ const XSS = {
         const cleaned = String(url).replace(/[\x00-\x1F\x7F]/g, '').trim();
         try {
             const parsed = new URL(cleaned, window.location.origin);
-            if (parsed.protocol === 'http:' || parsed.protocol === 'https:') {
-                return parsed.href;
-            }
+            if (parsed.protocol === 'http:' || parsed.protocol === 'https:') return parsed.href;
         } catch (e) {
-            if (cleaned.startsWith('/') && !cleaned.startsWith('//')) {
-                return cleaned;
-            }
+            if (cleaned.startsWith('/') && !cleaned.startsWith('//')) return cleaned;
         }
         return '';
     }
@@ -31,26 +25,73 @@ const XSS = {
 
 window.XSS = XSS;
 
+let _pendingConfirmForm = null;
+
+function showConfirmModal(message, onOk) {
+    const bodyEl = document.getElementById('confirmModalBody');
+    const okBtn  = document.getElementById('confirmModalOk');
+    if (!bodyEl || !okBtn) { if (onOk) onOk(); return; }
+    bodyEl.textContent = message;
+    const handler = function () {
+        okBtn.removeEventListener('click', handler);
+        bootstrap.Modal.getInstance(document.getElementById('confirmModal')).hide();
+        if (onOk) onOk();
+    };
+    okBtn.addEventListener('click', handler);
+    new bootstrap.Modal(document.getElementById('confirmModal')).show();
+}
+
+window.showConfirmModal = showConfirmModal;
+
+function setupFormSubmitOnce(form) {
+    form.addEventListener('submit', function () {
+        const btn = form.querySelector('[type=submit]');
+        if (!btn || btn.disabled) return;
+        btn.disabled = true;
+        const orig = btn.innerHTML;
+        btn.innerHTML = '<span class="spinner-border spinner-border-sm me-1" role="status" aria-hidden="true"></span>処理中...';
+        window.addEventListener('pageshow', function () {
+            btn.disabled = false;
+            btn.innerHTML = orig;
+        }, { once: true });
+    });
+}
+
+function showCopyFeedback(message) {
+    let el = document.getElementById('globalCopyFeedback');
+    if (!el) {
+        el = document.createElement('div');
+        el.id = 'globalCopyFeedback';
+        el.className = 'copy-feedback alert alert-success shadow-sm py-2 px-3';
+        document.body.appendChild(el);
+    }
+    el.textContent = message;
+    el.classList.add('show');
+    clearTimeout(el._timeout);
+    el._timeout = setTimeout(function () { el.classList.remove('show'); }, 2000);
+}
+
+window.showCopyFeedback = showCopyFeedback;
+
 document.addEventListener('DOMContentLoaded', function () {
     const alerts = document.querySelectorAll('.alert:not(.alert-danger):not(.modal .alert)');
     alerts.forEach(function (alert) {
         setTimeout(function () {
             alert.classList.add('fade');
-            setTimeout(function () {
-                alert.remove();
-            }, 150);
+            setTimeout(function () { alert.remove(); }, 150);
         }, 5000);
     });
 
-    const confirmForms = document.querySelectorAll('form[data-confirm]');
-    confirmForms.forEach(function (form) {
+    document.querySelectorAll('form[data-confirm]').forEach(function (form) {
         form.addEventListener('submit', function (e) {
-            if (!confirm(form.dataset.confirm)) {
-                e.preventDefault();
-            }
+            e.preventDefault();
+            const msg = form.dataset.confirm;
+            showConfirmModal(msg, function () { form.submit(); });
         });
     });
 
+    document.querySelectorAll('form:not([data-confirm])').forEach(setupFormSubmitOnce);
+
     const dueDateInput = document.getElementById('due_date');
     if (dueDateInput && !dueDateInput.value) {
         const tomorrow = new Date();
diff --git a/web/templates/admin/api_keys.html b/web/templates/admin/api_keys.html
index e9dc4fa..7270fdd 100644
--- a/web/templates/admin/api_keys.html
+++ b/web/templates/admin/api_keys.html
@@ -1,35 +1,38 @@
 {{template "base" .}}
 
 {{define "content"}}
-<h1 class="mb-4"><i class="bi bi-key me-2"></i>APIキー管理</h1>
+<h1 class="mb-4"><i class="bi bi-key me-2" aria-hidden="true"></i>APIキー管理</h1>
 
-{{if .error}}<div class="alert alert-danger">{{.error}}</div>{{end}}
+{{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
 
 {{if .newKey}}
-<div class="alert alert-success">
-    <h5 class="alert-heading"><i class="bi bi-check-circle me-2"></i>APIキーが作成されました</h5>
+<div class="alert alert-success" role="status">
+    <h5 class="alert-heading"><i class="bi bi-check-circle me-2" aria-hidden="true"></i>APIキーが作成されました</h5>
     <p class="mb-2">キー名: <strong>{{.newKeyName}}</strong></p>
     <p class="mb-0">以下のキーを安全な場所に保存してください。このキーは二度と表示されません。</p>
     <hr>
     <div class="d-flex align-items-center">
-        <code class="flex-grow-1 bg-dark text-light p-2 rounded me-2" id="newApiKey">{{.newKey}}</code>
-        <button class="btn btn-outline-secondary" onclick="copyKey()"><i class="bi bi-clipboard"></i></button>
+        <code class="flex-grow-1 bg-dark text-light p-2 rounded me-2" id="newApiKey" aria-label="APIキー">{{.newKey}}</code>
+        <button class="btn btn-outline-secondary" id="copyKeyBtn" aria-label="APIキーをコピー">
+            <i class="bi bi-clipboard" aria-hidden="true"></i>
+        </button>
     </div>
 </div>
 {{end}}
 
 <div class="card mb-4">
     <div class="card-header">
-        <i class="bi bi-plus-circle me-2"></i>新規APIキー作成
+        <i class="bi bi-plus-circle me-2" aria-hidden="true"></i>新規APIキー作成
     </div>
     <div class="card-body">
         <form action="/admin/api-keys" method="POST" class="row g-3">
             {{.csrfField}}
             <div class="col-md-8">
-                <input type="text" class="form-control" name="name" placeholder="キー名（例: 外部連携用）" required>
+                <label for="keyName" class="visually-hidden">キー名</label>
+                <input type="text" class="form-control" id="keyName" name="name" placeholder="キー名（例: 外部連携用）" required>
             </div>
             <div class="col-md-4">
-                <button type="submit" class="btn btn-primary w-100"><i class="bi bi-plus me-1"></i>作成</button>
+                <button type="submit" class="btn btn-primary w-100"><i class="bi bi-plus me-1" aria-hidden="true"></i>作成</button>
             </div>
         </form>
     </div>
@@ -37,31 +40,32 @@
 
 {{if .apiKeys}}
 <div class="table-responsive">
-    <table class="table table-hover">
+    <table class="table table-hover" aria-label="APIキー一覧">
         <thead class="table-light">
             <tr>
-                <th>ID</th>
-                <th>キー名</th>
-                <th>作成者</th>
-                <th>最終使用</th>
-                <th>作成日</th>
-                <th style="width: 100px">操作</th>
+                <th scope="col">ID</th>
+                <th scope="col">キー名</th>
+                <th scope="col">作成者</th>
+                <th scope="col">最終使用</th>
+                <th scope="col">作成日</th>
+                <th scope="col" style="width: 100px">操作</th>
             </tr>
         </thead>
         <tbody>
             {{range .apiKeys}}
             <tr>
                 <td>{{.ID}}</td>
-                <td><i class="bi bi-key me-1"></i>{{.Name}}</td>
+                <td><i class="bi bi-key me-1" aria-hidden="true"></i>{{.Name}}</td>
                 <td>{{if .User}}{{.User.Name}}{{else}}-{{end}}</td>
                 <td>{{if .LastUsed}}{{formatDateTime .LastUsed}}{{else}}<span class="text-muted">未使用</span>{{end}}</td>
                 <td>{{formatDate .CreatedAt}}</td>
                 <td>
                     <form action="/admin/api-keys/{{.ID}}/delete" method="POST" class="d-inline"
-                        onsubmit="return confirm('このAPIキーを削除しますか？')">
+                          data-confirm="このAPIキーを削除しますか？">
                         <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
-                        <button type="submit" class="btn btn-sm btn-outline-danger" title="削除"><i
-                                class="bi bi-trash"></i></button>
+                        <button type="submit" class="btn btn-sm btn-outline-danger" aria-label="{{.Name}}を削除">
+                            <i class="bi bi-trash" aria-hidden="true"></i>
+                        </button>
                     </form>
                 </td>
             </tr>
@@ -71,7 +75,7 @@
 </div>
 {{else}}
 <div class="text-center py-5">
-    <i class="bi bi-key display-1 text-muted"></i>
+    <i class="bi bi-key display-1 text-muted" aria-hidden="true"></i>
     <h3 class="mt-3">APIキーがありません</h3>
     <p class="text-muted">上のフォームから新しいAPIキーを作成してください。</p>
 </div>
@@ -79,12 +83,11 @@
 
 <div class="card mt-4">
     <div class="card-header">
-        <i class="bi bi-info-circle me-2"></i>API使用方法
+        <i class="bi bi-info-circle me-2" aria-hidden="true"></i>API使用方法
     </div>
     <div class="card-body">
         <p class="mb-2">APIにアクセスするには、<code>Authorization</code>ヘッダーにAPIキーを設定してください：</p>
-        <pre
-            class="bg-dark text-light p-3 rounded"><code>curl -H "Authorization: Bearer YOUR_API_KEY" http://localhost:8080/api/v1/assignments</code></pre>
+        <pre class="bg-dark text-light p-3 rounded"><code>curl -H "Authorization: Bearer YOUR_API_KEY" http://localhost:8080/api/v1/assignments</code></pre>
         <h6 class="mt-3">利用可能なエンドポイント：</h6>
         <ul class="mb-0">
             <li><code>GET /api/v1/assignments</code> - 課題一覧取得</li>
@@ -110,11 +113,20 @@
 
 {{define "scripts"}}
 <script>
-    function copyKey() {
-        const key = document.getElementById('newApiKey').innerText;
-        navigator.clipboard.writeText(key).then(() => {
-            alert('APIキーをコピーしました');
+    var copyKeyBtn = document.getElementById('copyKeyBtn');
+    if (copyKeyBtn) {
+        copyKeyBtn.addEventListener('click', function() {
+            var key = document.getElementById('newApiKey').textContent.trim();
+            if (!navigator.clipboard) {
+                showCopyFeedback('クリップボードがサポートされていません。手動でコピーしてください。');
+                return;
+            }
+            navigator.clipboard.writeText(key).then(function() {
+                showCopyFeedback('APIキーをコピーしました');
+            }).catch(function(err) {
+                showCopyFeedback('コピーに失敗しました: ' + (err.message || '不明なエラー'));
+            });
         });
     }
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/admin/users.html b/web/templates/admin/users.html
index 39b9908..1b89c9c 100644
--- a/web/templates/admin/users.html
+++ b/web/templates/admin/users.html
@@ -1,55 +1,68 @@
 {{template "base" .}}
 
 {{define "content"}}
-<h1 class="mb-4"><i class="bi bi-people me-2"></i>ユーザー管理</h1>
+<h1 class="mb-4"><i class="bi bi-people me-2" aria-hidden="true"></i>ユーザー管理</h1>
 
-{{if .error}}<div class="alert alert-danger">{{.error}}</div>{{end}}
+{{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
 
 {{if .users}}
 <div class="table-responsive">
-    <table class="table table-hover">
+    <table class="table table-hover" aria-label="ユーザー一覧">
         <thead class="table-light">
             <tr>
-                <th>ID</th>
-                <th>名前</th>
-                <th>メールアドレス</th>
-                <th>ロール</th>
-                <th>登録日</th>
-                <th style="width: 200px">操作</th>
+                <th scope="col">ID</th>
+                <th scope="col">名前</th>
+                <th scope="col">メールアドレス</th>
+                <th scope="col">ロール</th>
+                <th scope="col">登録日</th>
+                <th scope="col" style="width: 200px">操作</th>
             </tr>
         </thead>
         <tbody>
             {{range .users}}
-            <tr {{if eq .ID $.currentUserID}}class="table-primary" {{end}}>
+            <tr {{if eq .ID $.currentUserID}}class="table-primary"{{end}}>
                 <td>{{.ID}}</td>
                 <td>{{.Name}}{{if eq .ID $.currentUserID}}<span class="badge bg-info ms-2">自分</span>{{end}}</td>
                 <td>{{.Email}}</td>
-                <td>{{if eq .Role "admin"}}<span class="badge bg-danger">管理者</span>{{else}}<span
-                        class="badge bg-secondary">ユーザー</span>{{end}}</td>
+                <td>
+                    {{if eq .Role "admin"}}
+                    <span class="badge bg-danger">管理者</span>
+                    {{else}}
+                    <span class="badge bg-secondary">ユーザー</span>
+                    {{end}}
+                </td>
                 <td>{{formatDate .CreatedAt}}</td>
                 <td>
                     {{if ne .ID $.currentUserID}}
-                    <form action="/admin/users/{{.ID}}/role" method="POST" class="d-inline" {{if eq .Role "admin"
-                        }}onsubmit="return confirm('このユーザーを一般ユーザーに降格しますか？')"
-                        {{else}}onsubmit="return confirm('このユーザーを管理者に昇格しますか？')" {{end}}>
+                    {{if eq .Role "admin"}}
+                    <form action="/admin/users/{{.ID}}/role" method="POST" class="d-inline"
+                          data-confirm="このユーザーを一般ユーザーに降格しますか？">
                         <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
-                        {{if eq .Role "admin"}}
                         <input type="hidden" name="role" value="user">
-                        <button type="submit" class="btn btn-sm btn-outline-secondary" title="ユーザーに降格"><i
-                                class="bi bi-arrow-down"></i></button>
-                        {{else}}
-                        <input type="hidden" name="role" value="admin">
-                        <button type="submit" class="btn btn-sm btn-outline-warning" title="管理者に昇格"><i
-                                class="bi bi-arrow-up"></i></button>
-                        {{end}}
+                        <button type="submit" class="btn btn-sm btn-outline-secondary" aria-label="{{.Name}}をユーザーに降格">
+                            <i class="bi bi-arrow-down" aria-hidden="true"></i>
+                        </button>
                     </form>
-                    <form action="/admin/users/{{.ID}}/delete" method="POST" class="d-inline"
-                        onsubmit="return confirm('このユーザーを削除しますか？')">
+                    {{else}}
+                    <form action="/admin/users/{{.ID}}/role" method="POST" class="d-inline"
+                          data-confirm="このユーザーを管理者に昇格しますか？">
                         <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
-                        <button type="submit" class="btn btn-sm btn-outline-danger" title="削除"><i
-                                class="bi bi-trash"></i></button>
+                        <input type="hidden" name="role" value="admin">
+                        <button type="submit" class="btn btn-sm btn-outline-warning" aria-label="{{.Name}}を管理者に昇格">
+                            <i class="bi bi-arrow-up" aria-hidden="true"></i>
+                        </button>
                     </form>
-                    {{else}}<span class="text-muted">-</span>{{end}}
+                    {{end}}
+                    <form action="/admin/users/{{.ID}}/delete" method="POST" class="d-inline"
+                          data-confirm="このユーザーを削除しますか？">
+                        <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
+                        <button type="submit" class="btn btn-sm btn-outline-danger" aria-label="{{.Name}}を削除">
+                            <i class="bi bi-trash" aria-hidden="true"></i>
+                        </button>
+                    </form>
+                    {{else}}
+                    <span class="text-muted">-</span>
+                    {{end}}
                 </td>
             </tr>
             {{end}}
@@ -58,8 +71,8 @@
 </div>
 {{else}}
 <div class="text-center py-5">
-    <i class="bi bi-people display-1 text-muted"></i>
+    <i class="bi bi-people display-1 text-muted" aria-hidden="true"></i>
     <h3 class="mt-3">ユーザーがいません</h3>
 </div>
 {{end}}
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/assignments/edit.html b/web/templates/assignments/edit.html
index d4bf8f5..229bdb0 100644
--- a/web/templates/assignments/edit.html
+++ b/web/templates/assignments/edit.html
@@ -5,85 +5,71 @@
     <div class="col-lg-6">
         <div class="card shadow">
             <div class="card-header">
-                <h5 class="mb-0"><i class="bi bi-pencil me-2"></i>課題編集</h5>
+                <h5 class="mb-0"><i class="bi bi-pencil me-2" aria-hidden="true"></i>課題編集</h5>
             </div>
             <div class="card-body">
-                {{if .error}}<div class="alert alert-danger">{{.error}}</div>{{end}}
+                {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
                 <form method="POST" action="/assignments/{{.assignment.ID}}">
                     {{.csrfField}}
                     <div class="mb-3">
-                        <label for="title" class="form-label">タイトル <span class="text-danger">*</span></label>
-                        <input type="text" class="form-control" id="title" name="title" value="{{.assignment.Title}}"
-                            required>
+                        <label for="title" class="form-label">タイトル <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
+                        <input type="text" class="form-control" id="title" name="title" value="{{.assignment.Title}}" required>
                     </div>
                     <div class="mb-3">
                         <label for="subject" class="form-label">科目</label>
-                        <input type="text" class="form-control" id="subject" name="subject"
-                            value="{{.assignment.Subject}}">
+                        <input type="text" class="form-control" id="subject" name="subject" value="{{.assignment.Subject}}">
                     </div>
                     <div class="mb-3">
                         <label for="priority" class="form-label">重要度</label>
                         <select class="form-select" id="priority" name="priority">
-                            <option value="low" {{if eq .assignment.Priority "low" }}selected{{end}}>小</option>
-                            <option value="medium" {{if eq .assignment.Priority "medium" }}selected{{end}}>中</option>
-                            <option value="high" {{if eq .assignment.Priority "high" }}selected{{end}}>大</option>
+                            <option value="low"    {{if eq .assignment.Priority "low"   }}selected{{end}}>低</option>
+                            <option value="medium" {{if eq .assignment.Priority "medium"}}selected{{end}}>中</option>
+                            <option value="high"   {{if eq .assignment.Priority "high"  }}selected{{end}}>高</option>
                         </select>
                     </div>
                     <div class="mb-3">
-                        <label for="due_date" class="form-label">提出期限 <span class="text-danger">*</span></label>
-                        <input type="datetime-local" class="form-control" id="due_date" name="due_date"
-                            value="{{formatDateInput .assignment.DueDate}}" required>
+                        <label for="due_date" class="form-label">提出期限 <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
+                        <input type="datetime-local" class="form-control" id="due_date" name="due_date" value="{{formatDateInput .assignment.DueDate}}" required>
                     </div>
                     <div class="mb-3">
                         <label for="description" class="form-label">説明</label>
-                        <textarea class="form-control" id="description" name="description"
-                            rows="3">{{.assignment.Description}}</textarea>
+                        <textarea class="form-control" id="description" name="description" rows="3">{{.assignment.Description}}</textarea>
                     </div>
-                    <!-- 通知設定 -->
                     <div class="card bg-light mb-3">
                         <div class="card-body py-2">
-                            <h6 class="mb-2"><i class="bi bi-bell me-1"></i>通知設定</h6>
-                            <!-- 督促通知 -->
+                            <h6 class="mb-2"><i class="bi bi-bell me-1" aria-hidden="true"></i>通知設定</h6>
                             <div class="form-check form-switch mb-2">
-                                <input class="form-check-input" type="checkbox" id="urgent_reminder_enabled"
-                                    name="urgent_reminder_enabled" {{if
-                                    .assignment.UrgentReminderEnabled}}checked{{end}}>
+                                <input class="form-check-input" type="checkbox" id="urgent_reminder_enabled" name="urgent_reminder_enabled" {{if .assignment.UrgentReminderEnabled}}checked{{end}}>
                                 <label class="form-check-label" for="urgent_reminder_enabled">
                                     督促通知（期限3時間前から繰り返し通知）
                                 </label>
                             </div>
                             <div class="form-text small mb-2">
-                                重要度により間隔が変わります：大=10分、中=30分、小=1時間
+                                重要度により通知間隔が変わります：高=10分ごと、中=30分ごと、低=1時間ごと
                             </div>
                             <hr class="my-2">
                             <div class="form-check form-switch">
-                                <input class="form-check-input" type="checkbox" id="reminder_enabled"
-                                    name="reminder_enabled" {{if .assignment.ReminderEnabled}}checked{{end}}
-                                    onchange="toggleReminderDate(this)">
+                                <input class="form-check-input" type="checkbox" id="reminder_enabled" name="reminder_enabled" {{if .assignment.ReminderEnabled}}checked{{end}} onchange="toggleReminderDate(this)">
                                 <label class="form-check-label" for="reminder_enabled">
                                     リマインダー（指定日時に通知）
                                 </label>
                             </div>
-                            <div class="mt-2" id="reminder_at_group"
-                                style="display: {{if .assignment.ReminderEnabled}}block{{else}}none{{end}};">
+                            <div class="mt-2" id="reminder_at_group" style="display: {{if .assignment.ReminderEnabled}}block{{else}}none{{end}};">
                                 <label for="reminder_at" class="form-label small">通知日時</label>
-                                <input type="datetime-local" class="form-control form-control-sm" id="reminder_at"
-                                    name="reminder_at"
-                                    value="{{if .assignment.ReminderAt}}{{formatDateInput .assignment.ReminderAt}}{{end}}">
+                                <input type="datetime-local" class="form-control form-control-sm" id="reminder_at" name="reminder_at" value="{{if .assignment.ReminderAt}}{{formatDateInput .assignment.ReminderAt}}{{end}}">
                                 {{if .assignment.ReminderSent}}
-                                <div class="text-success small mt-1"><i class="bi bi-check-circle me-1"></i>通知送信済み</div>
+                                <div class="text-success small mt-1"><i class="bi bi-check-circle me-1" aria-hidden="true"></i>通知送信済み</div>
                                 {{end}}
                             </div>
                         </div>
                     </div>
                     {{if .recurring}}
-                    <!-- 繰り返し設定 -->
                     <div class="card bg-light mb-3">
                         <div class="card-body py-2">
                             <div class="d-flex justify-content-between align-items-center mb-2">
-                                <h6 class="mb-0"><i class="bi bi-arrow-repeat me-1"></i>繰り返し設定</h6>
+                                <h6 class="mb-0"><i class="bi bi-arrow-repeat me-1" aria-hidden="true"></i>繰り返し設定</h6>
                                 <a href="/recurring/{{.recurring.ID}}/edit" class="btn btn-sm btn-outline-primary">
-                                    <i class="bi bi-pencil me-1"></i>編集
+                                    <i class="bi bi-pencil me-1" aria-hidden="true"></i>編集
                                 </a>
                             </div>
                             <div class="row">
@@ -110,7 +96,7 @@
                     </div>
                     {{end}}
                     <div class="d-flex gap-2">
-                        <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1"></i>更新</button>
+                        <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1" aria-hidden="true"></i>更新</button>
                         <a href="/assignments" class="btn btn-outline-secondary">キャンセル</a>
                     </div>
                 </form>
@@ -123,4 +109,4 @@
         document.getElementById('reminder_at_group').style.display = checkbox.checked ? 'block' : 'none';
     }
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/assignments/index.html b/web/templates/assignments/index.html
index 82ccaa7..5d29115 100644
--- a/web/templates/assignments/index.html
+++ b/web/templates/assignments/index.html
@@ -2,132 +2,100 @@
 
 {{define "content"}}
 <div class="d-flex justify-content-between align-items-center mb-3">
-    <div class="d-flex align-items-center">
-        <h4 class="mb-0 fw-bold"><i class="bi bi-list-task me-2"></i>課題一覧</h4>
-    </div>
+    <h4 class="mb-0 fw-bold"><i class="bi bi-list-task me-2" aria-hidden="true"></i>課題一覧</h4>
     <div class="d-flex gap-2">
-        <button class="btn btn-sm btn-secondary text-white" onclick="toggleCountdown()" id="toggleCountdownBtn">
-            <i class="bi bi-clock me-1"></i><span id="countdownBtnText">カウントダウン表示中</span>
+        <button class="btn btn-sm btn-secondary text-white" onclick="toggleCountdown()" id="toggleCountdownBtn" aria-pressed="false">
+            <i class="bi bi-clock me-1" aria-hidden="true"></i><span id="countdownBtnText">カウントダウンを非表示</span>
         </button>
         <a href="/assignments/new" class="btn btn-sm btn-primary">
-            <i class="bi bi-plus-lg me-1"></i>新規登録
+            <i class="bi bi-plus-lg me-1" aria-hidden="true"></i>新規登録
         </a>
     </div>
 </div>
 
-<!-- Tabs -->
-<ul class="nav nav-tabs border-0 mb-2" id="assignmentTabs">
-    <li class="nav-item">
-        <a class="nav-link py-2 rounded-0 {{if eq .filter "pending"}}fw-bold border-bottom border-dark border-3
-            text-dark{{else}}border-0 text-muted{{end}}"
-            href="/assignments?filter=pending&q={{.query}}&priority={{.priority}}">
-            未完了
-        </a>
+<ul class="nav nav-tabs border-0 mb-2" id="assignmentTabs" role="tablist">
+    <li class="nav-item" role="presentation">
+        <a class="nav-link py-2 rounded-0 {{if eq .filter "pending"}}fw-bold border-bottom border-dark border-3 text-dark{{else}}border-0 text-muted{{end}}"
+            href="/assignments?filter=pending&q={{.query}}&priority={{.priority}}">未完了</a>
     </li>
-
-    <li class="nav-item">
-        <a class="nav-link py-2 rounded-0 {{if eq .filter "due_today"}}fw-bold border-bottom border-dark border-3
-            text-dark{{else}}border-0 text-muted{{end}}"
-            href="/assignments?filter=due_today&q={{.query}}&priority={{.priority}}">
-            今日が期限
-        </a>
+    <li class="nav-item" role="presentation">
+        <a class="nav-link py-2 rounded-0 {{if eq .filter "due_today"}}fw-bold border-bottom border-dark border-3 text-dark{{else}}border-0 text-muted{{end}}"
+            href="/assignments?filter=due_today&q={{.query}}&priority={{.priority}}">今日が期限</a>
     </li>
-
-    <li class="nav-item">
-        <a class="nav-link py-2 rounded-0 {{if eq .filter "due_this_week"}}fw-bold border-bottom border-dark border-3
-            text-dark{{else}}border-0 text-muted{{end}}"
-            href="/assignments?filter=due_this_week&q={{.query}}&priority={{.priority}}">
-            今週が期限
-        </a>
+    <li class="nav-item" role="presentation">
+        <a class="nav-link py-2 rounded-0 {{if eq .filter "due_this_week"}}fw-bold border-bottom border-dark border-3 text-dark{{else}}border-0 text-muted{{end}}"
+            href="/assignments?filter=due_this_week&q={{.query}}&priority={{.priority}}">今週が期限</a>
     </li>
-
-    <li class="nav-item">
-        <a class="nav-link py-2 rounded-0 {{if eq .filter "completed"}}fw-bold border-bottom border-dark border-3
-            text-dark{{else}}border-0 text-muted{{end}}"
-            href="/assignments?filter=completed&q={{.query}}&priority={{.priority}}">
-            完了済み
-        </a>
+    <li class="nav-item" role="presentation">
+        <a class="nav-link py-2 rounded-0 {{if eq .filter "completed"}}fw-bold border-bottom border-dark border-3 text-dark{{else}}border-0 text-muted{{end}}"
+            href="/assignments?filter=completed&q={{.query}}&priority={{.priority}}">完了済み</a>
     </li>
-
-    <li class="nav-item">
-        <a class="nav-link py-2 rounded-0 {{if eq .filter "overdue"}}fw-bold border-bottom border-dark border-3
-            text-dark{{else}}border-0 text-muted{{end}}"
-            href="/assignments?filter=overdue&q={{.query}}&priority={{.priority}}">
-            期限切れ
-        </a>
+    <li class="nav-item" role="presentation">
+        <a class="nav-link py-2 rounded-0 {{if eq .filter "overdue"}}fw-bold border-bottom border-dark border-3 text-dark{{else}}border-0 text-muted{{end}}"
+            href="/assignments?filter=overdue&q={{.query}}&priority={{.priority}}">期限切れ</a>
     </li>
-
-    <li class="nav-item">
-        <a class="nav-link py-2 rounded-0 border-0 text-muted"
-            href="/recurring">
-            繰り返し
+    <li class="nav-item ms-auto" role="presentation">
+        <a class="nav-link py-2 rounded-0 border-0 text-muted" href="/recurring">
+            <i class="bi bi-arrow-repeat me-1" aria-hidden="true"></i>繰り返し管理
         </a>
     </li>
 </ul>
 <hr class="mt-0 mb-3 text-muted" style="opacity: 0.1;">
 
-<!-- Filter Section -->
-<form action="/assignments" method="GET" class="row g-2 mb-3 align-items-center">
+<form action="/assignments" method="GET" class="row g-2 mb-3 align-items-center" role="search">
     <input type="hidden" name="filter" value="{{.filter}}">
     <div class="col-md-5">
         <div class="input-group input-group-sm">
-            <span class="input-group-text bg-white border-end-0 text-muted"><i class="bi bi-search"></i></span>
-            <input type="text" class="form-control border-start-0 ps-0 bg-white" name="q" placeholder="検索..."
-                value="{{.query}}">
+            <span class="input-group-text bg-white border-end-0 text-muted"><i class="bi bi-search" aria-hidden="true"></i></span>
+            <label for="searchInput" class="visually-hidden">課題を検索</label>
+            <input type="text" class="form-control border-start-0 ps-0 bg-white" id="searchInput" name="q" placeholder="検索..." value="{{.query}}">
         </div>
     </div>
     <div class="col-md-4">
-        <select class="form-select form-select-sm bg-white" name="priority" onchange="this.form.submit()">
+        <label for="priorityFilter" class="visually-hidden">重要度で絞り込み</label>
+        <select class="form-select form-select-sm bg-white" id="priorityFilter" name="priority" onchange="this.form.submit()">
             <option value="">全ての重要度</option>
-            <option value="high" {{if eq .priority "high" }}selected{{end}}>高</option>
-            <option value="medium" {{if eq .priority "medium" }}selected{{end}}>中</option>
-            <option value="low" {{if eq .priority "low" }}selected{{end}}>低</option>
+            <option value="high"   {{if eq .priority "high"  }}selected{{end}}>高</option>
+            <option value="medium" {{if eq .priority "medium"}}selected{{end}}>中</option>
+            <option value="low"    {{if eq .priority "low"   }}selected{{end}}>低</option>
         </select>
     </div>
     <div class="col-md-3">
-        <a href="/assignments?filter={{.filter}}" class="btn btn-sm btn-outline-secondary w-100 bg-white">
-            クリア
-        </a>
+        <a href="/assignments?filter={{.filter}}" class="btn btn-sm btn-outline-secondary w-100 bg-white">クリア</a>
     </div>
 </form>
 
-<!-- Table -->
 <div class="card shadow-sm border-0 rounded-0">
     <div class="card-body p-0">
         <div class="table-responsive">
-            <table class="table table-hover align-middle mb-0 custom-table">
+            <table class="table table-hover align-middle mb-0 custom-table" aria-label="課題一覧">
                 <thead class="bg-secondary-subtle">
                     <tr>
-                        <th style="width: 50px;" class="ps-3 text-center text-dark fw-bold">状態</th>
-                        <th style="width: 120px;" class="text-dark fw-bold">科目</th>
-                        <th style="width: 80px;" class="text-dark fw-bold">重要度</th>
-                        <th class="text-dark fw-bold">タイトル</th>
-                        <th style="width: 140px;" class="text-dark fw-bold">期限</th>
-                        <th style="width: 120px;" class="countdown-col text-dark fw-bold">残り</th>
-                        <th style="width: 80px;" class="text-end pe-3 text-dark fw-bold">操作</th>
+                        <th scope="col" style="width: 50px;" class="ps-3 text-center text-dark fw-bold">状態</th>
+                        <th scope="col" style="width: 120px;" class="text-dark fw-bold">科目</th>
+                        <th scope="col" style="width: 80px;" class="text-dark fw-bold">重要度</th>
+                        <th scope="col" class="text-dark fw-bold">タイトル</th>
+                        <th scope="col" style="width: 140px;" class="text-dark fw-bold">期限</th>
+                        <th scope="col" style="width: 120px;" class="countdown-col text-dark fw-bold">残り</th>
+                        <th scope="col" style="width: 80px;" class="text-end pe-3 text-dark fw-bold">操作</th>
                     </tr>
                 </thead>
                 <tbody>
                     {{range .assignments}}
-                    <tr class="assignment-row border-bottom" data-due-ts="{{.DueDate.Unix}}"
-                        data-completed="{{.IsCompleted}}">
+                    <tr class="assignment-row border-bottom" data-due-ts="{{.DueDate.Unix}}" data-completed="{{.IsCompleted}}">
                         <td class="ps-3 text-center">
                             {{if .IsCompleted}}
                             <form action="/assignments/{{.ID}}/toggle" method="POST" class="d-inline">
                                 <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
-                                <button type="submit"
-                                    class="btn btn-link p-0 text-success text-decoration-none hover-dark"
-                                    title="未完了に戻す">
-                                    <i class="bi bi-check-circle-fill"></i>
+                                <button type="submit" class="btn btn-link p-0 text-success text-decoration-none btn-touch" aria-label="未完了に戻す">
+                                    <i class="bi bi-check-circle-fill" aria-hidden="true"></i>
                                 </button>
                             </form>
                             {{else}}
                             <form action="/assignments/{{.ID}}/toggle" method="POST" class="d-inline">
                                 <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
-                                <button type="submit"
-                                    class="btn btn-link p-0 text-secondary text-decoration-none hover-dark"
-                                    title="完了にする">
-                                    <i class="bi bi-circle"></i>
+                                <button type="submit" class="btn btn-link p-0 text-secondary text-decoration-none btn-touch" aria-label="完了にする">
+                                    <i class="bi bi-circle" aria-hidden="true"></i>
                                 </button>
                             </form>
                             {{end}}
@@ -135,57 +103,54 @@
                         <td><span class="badge bg-secondary text-white border-0 fw-bold">{{.Subject}}</span></td>
                         <td>
                             {{if eq .Priority "high"}}
-                            <span class="badge bg-danger text-white border-0 fw-bold small">高</span>
+                            <span class="badge bg-danger text-white border-0 fw-bold small">高<span class="visually-hidden">（重要度：高）</span></span>
                             {{else if eq .Priority "medium"}}
-                            <span class="badge bg-warning text-dark border-0 fw-bold small">中</span>
+                            <span class="badge bg-warning text-dark border-0 fw-bold small">中<span class="visually-hidden">（重要度：中）</span></span>
                             {{else}}
-                            <span class="badge bg-dark text-white border-0 fw-bold small">低</span>
+                            <span class="badge bg-dark text-white border-0 fw-bold small">低<span class="visually-hidden">（重要度：低）</span></span>
                             {{end}}
                         </td>
                         <td>
                             <div class="d-flex align-items-center">
                                 <div class="fw-bold text-dark text-truncate" style="max-width: 280px;">{{.Title}}</div>
                                 {{if .RecurringAssignmentID}}
-                                <button type="button" class="btn btn-link p-0 ms-2 text-info" data-bs-toggle="modal"
-                                    data-bs-target="#recurringModal" data-recurring-id="{{.RecurringAssignmentID}}"
+                                <button type="button" class="btn btn-link p-0 ms-2 text-info btn-touch" data-bs-toggle="modal"
+                                    data-bs-target="#recurringModal"
+                                    data-recurring-id="{{.RecurringAssignmentID}}"
                                     data-assignment-id="{{.ID}}"
                                     data-recurring-title="{{.Title}}"
                                     data-recurring-type="{{if .RecurringAssignment}}{{.RecurringAssignment.RecurrenceType}}{{else}}unknown{{end}}"
                                     data-recurring-active="{{if .RecurringAssignment}}{{.RecurringAssignment.IsActive}}{{else}}true{{end}}"
-                                    title="繰り返し課題">
-                                    <i class="fa-solid fa-repeat"></i>
+                                    aria-label="繰り返し設定を表示">
+                                    <i class="bi bi-repeat" aria-hidden="true"></i>
                                 </button>
                                 {{end}}
                             </div>
                         </td>
                         <td>
-                            <div class="small fw-bold text-dark user-select-all">{{.DueDate.Format "2006/01/02 15:04"}}
-                            </div>
+                            <div class="small fw-bold text-dark user-select-all">{{.DueDate.Format "2006/01/02 15:04"}}</div>
                         </td>
                         <td class="countdown-col">
                             {{if not .IsCompleted}}
-                            <span class="countdown small fw-bold font-monospace text-dark">...</span>
+                            <span class="countdown small fw-bold font-monospace text-dark" aria-live="off">...</span>
                             {{else}}
                             <span class="text-secondary small fw-bold">-</span>
                             {{end}}
                         </td>
                         <td class="text-end pe-3">
-                            <div class="btn-group">
-                                <a href="/assignments/{{.ID}}/edit" class="text-primary me-3 text-decoration-none">
-                                    <i class="bi bi-pencil-fill"></i>
+                            <div class="d-flex justify-content-end gap-2">
+                                <a href="/assignments/{{.ID}}/edit" class="text-primary text-decoration-none btn-touch d-inline-flex align-items-center" aria-label="編集">
+                                    <i class="bi bi-pencil-fill" aria-hidden="true"></i>
                                 </a>
                                 {{if .RecurringAssignmentID}}
-                                <button type="button" class="btn btn-link p-0 text-danger text-decoration-none border-0 bg-transparent"
-                                    onclick="showDeleteRecurringModal({{.ID}}, {{.RecurringAssignmentID}})">
-                                    <i class="bi bi-trash-fill"></i>
+                                <button type="button" class="btn btn-link p-0 text-danger text-decoration-none border-0 bg-transparent btn-touch" onclick="showDeleteRecurringModal({{.ID}}, {{.RecurringAssignmentID}})" aria-label="削除">
+                                    <i class="bi bi-trash-fill" aria-hidden="true"></i>
                                 </button>
                                 {{else}}
-                                <form action="/assignments/{{.ID}}/delete" method="POST" class="d-inline"
-                                    onsubmit="return confirm('削除しますか？');">
+                                <form action="/assignments/{{.ID}}/delete" method="POST" class="d-inline" data-confirm="削除しますか？">
                                     <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
-                                    <button type="submit"
-                                        class="btn btn-link p-0 text-danger text-decoration-none border-0 bg-transparent">
-                                        <i class="bi bi-trash-fill"></i>
+                                    <button type="submit" class="btn btn-link p-0 text-danger text-decoration-none border-0 bg-transparent btn-touch" aria-label="削除">
+                                        <i class="bi bi-trash-fill" aria-hidden="true"></i>
                                     </button>
                                 </form>
                                 {{end}}
@@ -194,8 +159,12 @@
                     </tr>
                     {{else}}
                     <tr>
-                        <td colspan="7" class="text-center py-4 text-secondary fw-bold small">
-                            課題なし
+                        <td colspan="7" class="text-center py-5">
+                            <i class="bi bi-inbox display-4 text-muted" aria-hidden="true"></i>
+                            <p class="mt-2 mb-1 text-muted fw-bold">課題がありません</p>
+                            <a href="/assignments/new" class="btn btn-sm btn-primary mt-1">
+                                <i class="bi bi-plus-lg me-1" aria-hidden="true"></i>課題を登録する
+                            </a>
                         </td>
                     </tr>
                     {{end}}
@@ -205,21 +174,19 @@
     </div>
     {{if gt .totalPages 1}}
     <div class="card-footer bg-white border-top-0 py-2">
-        <nav>
+        <nav aria-label="ページナビゲーション">
             <ul class="pagination pagination-sm justify-content-center mb-0">
                 <li class="page-item {{if not .hasPrev}}disabled{{end}}">
-                    <a class="page-link border-0 text-secondary"
-                        href="/assignments?page={{.prevPage}}&filter={{.filter}}&q={{.query}}&priority={{.priority}}">
-                        <i class="bi bi-chevron-left"></i>
+                    <a class="page-link border-0 text-secondary" href="/assignments?page={{.prevPage}}&filter={{.filter}}&q={{.query}}&priority={{.priority}}" aria-label="前のページ">
+                        <i class="bi bi-chevron-left" aria-hidden="true"></i>
                     </a>
                 </li>
                 <li class="page-item disabled">
-                    <span class="page-link border-0 text-dark fw-bold">{{.currentPage}} / {{.totalPages}}</span>
+                    <span class="page-link border-0 text-dark fw-bold" aria-current="page">{{.currentPage}} / {{.totalPages}}</span>
                 </li>
                 <li class="page-item {{if not .hasNext}}disabled{{end}}">
-                    <a class="page-link border-0 text-secondary"
-                        href="/assignments?page={{.nextPage}}&filter={{.filter}}&q={{.query}}&priority={{.priority}}">
-                        <i class="bi bi-chevron-right"></i>
+                    <a class="page-link border-0 text-secondary" href="/assignments?page={{.nextPage}}&filter={{.filter}}&q={{.query}}&priority={{.priority}}" aria-label="次のページ">
+                        <i class="bi bi-chevron-right" aria-hidden="true"></i>
                     </a>
                 </li>
             </ul>
@@ -229,121 +196,119 @@
 </div>
 
 <script>
+    var _countdownInterval = null;
+
     function updateCountdowns() {
-        const now = new Date();
-        document.querySelectorAll('.assignment-row').forEach(row => {
+        var now = new Date();
+        var hasUnder24h = false;
+
+        document.querySelectorAll('.assignment-row').forEach(function(row) {
             if (row.getAttribute('data-completed') === 'true') return;
-
-            const dueTs = row.getAttribute('data-due-ts');
+            var dueTs = row.getAttribute('data-due-ts');
             if (!dueTs) return;
-
-            // Fix: Use timestamp directly to avoid parsing issues
-            const due = new Date(parseInt(dueTs) * 1000);
+            var due = new Date(parseInt(dueTs) * 1000);
             if (isNaN(due.getTime())) return;
 
-            const diff = due - now;
-            const countdownEl = row.querySelector('.countdown');
+            var diff = due - now;
+            var countdownEl = row.querySelector('.countdown');
 
-            // Reset classes
             row.classList.remove('anxiety-danger', 'anxiety-warning', 'bg-danger-subtle');
             if (countdownEl) countdownEl.className = 'countdown small fw-bold font-monospace';
 
             if (diff < 0) {
                 if (countdownEl) {
-                    countdownEl.textContent = "期限切れ";
+                    countdownEl.textContent = '期限切れ';
                     countdownEl.classList.add('text-danger');
                 }
                 row.classList.add('bg-danger-subtle');
                 return;
             }
 
-            const days = Math.floor(diff / (1000 * 60 * 60 * 24));
-            const hours = Math.floor((diff % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
-            const minutes = Math.floor((diff % (1000 * 60 * 60)) / (1000 * 60));
-            const seconds = Math.floor((diff % (1000 * 60)) / 1000);
+            var days    = Math.floor(diff / 86400000);
+            var hours   = Math.floor((diff % 86400000) / 3600000);
+            var minutes = Math.floor((diff % 3600000) / 60000);
+            var seconds = Math.floor((diff % 60000) / 1000);
+            var remainingHours = days * 24 + hours;
 
-            let text = "";
-            let remainingHours = (days * 24) + hours;
-
-            if (days > 0) {
-                text += `${days}日 `;
-            }
-            text += `${String(hours).padStart(2, '0')}:${String(minutes).padStart(2, '0')}:${String(seconds).padStart(2, '0')}`;
+            var text = (days > 0 ? days + '日 ' : '') +
+                String(hours).padStart(2, '0') + ':' +
+                String(minutes).padStart(2, '0') + ':' +
+                String(seconds).padStart(2, '0');
 
             if (countdownEl) countdownEl.textContent = text;
 
-            // Anxiety Logic
             if (remainingHours < 24) {
+                hasUnder24h = true;
                 row.classList.add('anxiety-danger');
                 if (countdownEl) {
                     countdownEl.classList.add('text-danger', 'countdown-urgent');
-                    countdownEl.innerHTML = '<i class="bi bi-exclamation-triangle-fill me-1"></i>' + text;
+                    countdownEl.innerHTML = '<i class="bi bi-exclamation-triangle-fill me-1" aria-hidden="true"></i>' + text;
                 }
             } else if (days < 7) {
                 row.classList.add('anxiety-warning');
                 if (countdownEl) {
                     countdownEl.classList.add('text-dark');
-                    countdownEl.innerHTML = '<i class="bi bi-exclamation-triangle-fill text-warning me-1"></i>' + text;
+                    countdownEl.innerHTML = '<i class="bi bi-exclamation-triangle-fill text-warning me-1" aria-hidden="true"></i>' + text;
                 }
             } else {
                 if (countdownEl) countdownEl.classList.add('text-secondary');
             }
         });
+
+        scheduleNextUpdate(hasUnder24h);
+    }
+
+    function scheduleNextUpdate(hasUnder24h) {
+        if (_countdownInterval !== null) return;
+        var interval = hasUnder24h ? 1000 : 60000;
+        _countdownInterval = setTimeout(function() {
+            _countdownInterval = null;
+            updateCountdowns();
+        }, interval);
     }
 
     function toggleCountdown() {
-        const cols = document.querySelectorAll('.countdown-col');
-        const btnText = document.getElementById('countdownBtnText');
-        const isHidden = cols[0] && cols[0].style.display === 'none';
+        var cols = document.querySelectorAll('.countdown-col');
+        var btn  = document.getElementById('toggleCountdownBtn');
+        var btnText = document.getElementById('countdownBtnText');
+        var isHidden = cols[0] && cols[0].style.display === 'none';
 
-        cols.forEach(col => {
-            col.style.display = isHidden ? '' : 'none';
-        });
+        cols.forEach(function(col) { col.style.display = isHidden ? '' : 'none'; });
 
-        btnText.textContent = isHidden ? 'カウントダウン表示中' : 'カウントダウン非表示中';
-        localStorage.setItem('countdownHidden', !isHidden);
+        var nowHidden = !isHidden;
+        btnText.textContent = nowHidden ? 'カウントダウンを表示' : 'カウントダウンを非表示';
+        btn.setAttribute('aria-pressed', nowHidden ? 'true' : 'false');
+        localStorage.setItem('countdownHidden', nowHidden);
     }
 
-    // Init with higher frequency for smooth panic
-    setInterval(updateCountdowns, 1000);
     updateCountdowns();
 
-    // Check preference
-    const isHidden = localStorage.getItem('countdownHidden') === 'true';
-    if (isHidden) {
-        document.querySelectorAll('.countdown-col').forEach(col => {
-            col.style.display = 'none';
-        });
-        const btnText = document.getElementById('countdownBtnText');
-        if (btnText) btnText.textContent = 'カウントダウン非表示中';
+    if (localStorage.getItem('countdownHidden') === 'true') {
+        document.querySelectorAll('.countdown-col').forEach(function(col) { col.style.display = 'none'; });
+        var btn = document.getElementById('toggleCountdownBtn');
+        var btnText = document.getElementById('countdownBtnText');
+        if (btnText) btnText.textContent = 'カウントダウンを表示';
+        if (btn) btn.setAttribute('aria-pressed', 'true');
     }
 
-    // Recurring modal handler - wait for DOM to be ready
     document.addEventListener('DOMContentLoaded', function() {
-        const recurringModal = document.getElementById('recurringModal');
+        var recurringModal = document.getElementById('recurringModal');
         if (recurringModal) {
-            recurringModal.addEventListener('show.bs.modal', function (event) {
-                const button = event.relatedTarget;
-                const id = button.getAttribute('data-recurring-id');
-                const assignmentId = button.getAttribute('data-assignment-id');
-                const title = button.getAttribute('data-recurring-title');
-                const type = button.getAttribute('data-recurring-type');
-                const isActive = button.getAttribute('data-recurring-active') === 'true';
+            recurringModal.addEventListener('show.bs.modal', function(event) {
+                var button = event.relatedTarget;
+                var id         = button.getAttribute('data-recurring-id');
+                var title      = button.getAttribute('data-recurring-title');
+                var type       = button.getAttribute('data-recurring-type');
+                var isActive   = button.getAttribute('data-recurring-active') === 'true';
 
                 document.getElementById('recurringModalTitle').textContent = title;
                 document.getElementById('recurringStopForm').action = '/recurring/' + id + '/stop';
                 document.getElementById('recurringEditBtn').href = '/recurring/' + id + '/edit';
 
-                const typeLabels = {
-                    'daily': '毎日',
-                    'weekly': '毎週',
-                    'monthly': '毎月',
-                    'unknown': '(読み込み中...)'
-                };
+                var typeLabels = { daily: '毎日', weekly: '毎週', monthly: '毎月', unknown: '(不明)' };
                 document.getElementById('recurringTypeLabel').textContent = typeLabels[type] || type || '不明';
 
-
-                const statusEl = document.getElementById('recurringStatus');
+                var statusEl = document.getElementById('recurringStatus');
                 if (isActive) {
                     statusEl.innerHTML = '<span class="badge bg-success">有効</span>';
                     document.getElementById('recurringStopBtn').style.display = 'inline-block';
@@ -356,43 +321,41 @@
     });
 </script>
 
-<!-- Recurring Modal -->
-<div class="modal fade" id="recurringModal" tabindex="-1">
+<div class="modal fade" id="recurringModal" tabindex="-1" aria-labelledby="recurringModalHeading" aria-modal="true" role="dialog">
     <div class="modal-dialog">
         <div class="modal-content">
             <div class="modal-header">
-                <h5 class="modal-title"><i class="fa-solid fa-repeat me-2"></i>繰り返し課題</h5>
-                <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
+                <h5 class="modal-title" id="recurringModalHeading"><i class="bi bi-repeat me-2" aria-hidden="true"></i>繰り返し課題</h5>
+                <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="閉じる"></button>
             </div>
             <div class="modal-body">
                 <h6 id="recurringModalTitle" class="mb-3 fw-bold"></h6>
                 <table class="table table-sm table-borderless">
                     <tbody>
                         <tr>
-                            <th class="text-muted" style="width: 100px;">繰り返し</th>
+                            <th class="text-muted" style="width: 100px;" scope="row">繰り返し</th>
                             <td id="recurringTypeLabel">読み込み中...</td>
                         </tr>
                         <tr>
-                            <th class="text-muted">状態</th>
+                            <th class="text-muted" scope="row">状態</th>
                             <td id="recurringStatus">読み込み中...</td>
                         </tr>
                     </tbody>
                 </table>
-                <div class="alert alert-info small mb-0">
-                    <i class="bi bi-info-circle me-1"></i>
+                <div class="alert alert-info small mb-0" role="note">
+                    <i class="bi bi-info-circle me-1" aria-hidden="true"></i>
                     繰り返しを停止すると、今後新しい課題は自動作成されなくなります。既存の課題はそのまま残ります。
                 </div>
             </div>
             <div class="modal-footer">
                 <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">閉じる</button>
                 <a id="recurringEditBtn" href="#" class="btn btn-primary">
-                    <i class="bi bi-pencil me-1"></i>編集
+                    <i class="bi bi-pencil me-1" aria-hidden="true"></i>編集
                 </a>
-                <form id="recurringStopForm" method="POST" class="d-inline">
+                <form id="recurringStopForm" method="POST" class="d-inline" data-confirm="繰り返しを停止しますか？">
                     <input type="hidden" name="_csrf" value="{{.csrfToken}}">
-                    <button type="submit" id="recurringStopBtn" class="btn btn-danger"
-                        onclick="return confirm('繰り返しを停止しますか？');">
-                        <i class="bi bi-stop-fill me-1"></i>停止
+                    <button type="submit" id="recurringStopBtn" class="btn btn-danger">
+                        <i class="bi bi-stop-fill me-1" aria-hidden="true"></i>停止
                     </button>
                 </form>
             </div>
@@ -400,13 +363,12 @@
     </div>
 </div>
 
-<!-- Delete Recurring Confirmation Modal -->
-<div class="modal fade" id="deleteRecurringModal" tabindex="-1">
+<div class="modal fade" id="deleteRecurringModal" tabindex="-1" aria-labelledby="deleteRecurringModalHeading" aria-modal="true" role="dialog">
     <div class="modal-dialog">
         <div class="modal-content">
             <div class="modal-header">
-                <h5 class="modal-title"><i class="bi bi-trash me-2"></i>繰り返し課題の削除</h5>
-                <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
+                <h5 class="modal-title" id="deleteRecurringModalHeading"><i class="bi bi-trash me-2" aria-hidden="true"></i>繰り返し課題の削除</h5>
+                <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="閉じる"></button>
             </div>
             <div class="modal-body">
                 <p>この課題は繰り返し設定に関連付けられています。</p>
@@ -416,15 +378,11 @@
                 <button type="button" class="btn btn-secondary" data-bs-dismiss="modal">キャンセル</button>
                 <form id="deleteOnlyForm" method="POST" class="d-inline">
                     <input type="hidden" name="_csrf" value="{{.csrfToken}}">
-                    <button type="submit" class="btn btn-outline-danger">
-                        課題のみ削除
-                    </button>
+                    <button type="submit" class="btn btn-outline-danger">課題のみ削除</button>
                 </form>
                 <form id="deleteAndStopForm" method="POST" class="d-inline">
                     <input type="hidden" name="_csrf" value="{{.csrfToken}}">
-                    <button type="submit" class="btn btn-danger">
-                        削除して繰り返しも削除
-                    </button>
+                    <button type="submit" class="btn btn-danger">削除して繰り返しも削除</button>
                 </form>
             </div>
         </div>
@@ -432,11 +390,11 @@
 </div>
 
 <script>
-function showDeleteRecurringModal(assignmentId, recurringId) {
-    var modal = new bootstrap.Modal(document.getElementById('deleteRecurringModal'));
-    document.getElementById('deleteOnlyForm').action = '/assignments/' + assignmentId + '/delete';
-    document.getElementById('deleteAndStopForm').action = '/assignments/' + assignmentId + '/delete?stop_recurring=' + recurringId;
-    modal.show();
-}
+    function showDeleteRecurringModal(assignmentId, recurringId) {
+        var modal = new bootstrap.Modal(document.getElementById('deleteRecurringModal'));
+        document.getElementById('deleteOnlyForm').action = '/assignments/' + assignmentId + '/delete';
+        document.getElementById('deleteAndStopForm').action = '/assignments/' + assignmentId + '/delete?stop_recurring=' + recurringId;
+        modal.show();
+    }
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/assignments/new.html b/web/templates/assignments/new.html
index fa1ab82..3a0e5ac 100644
--- a/web/templates/assignments/new.html
+++ b/web/templates/assignments/new.html
@@ -5,83 +5,71 @@
     <div class="col-lg-6">
         <div class="card shadow">
             <div class="card-header">
-                <h5 class="mb-0"><i class="bi bi-plus-circle me-2"></i>課題登録</h5>
+                <h5 class="mb-0"><i class="bi bi-plus-circle me-2" aria-hidden="true"></i>課題登録</h5>
             </div>
             <div class="card-body">
-                {{if .error}}<div class="alert alert-danger">{{.error}}</div>{{end}}
+                {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
                 <form method="POST" action="/assignments">
                     {{.csrfField}}
                     <div class="mb-3">
-                        <label for="title" class="form-label">タイトル <span class="text-danger">*</span></label>
-                        <input type="text" class="form-control" id="title" name="title" value="{{.formTitle}}" required
-                            autofocus>
+                        <label for="title" class="form-label">タイトル <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
+                        <input type="text" class="form-control" id="title" name="title" value="{{.formTitle}}" required autofocus>
                     </div>
                     <div class="mb-3">
                         <label for="subject" class="form-label">科目</label>
-                        <input type="text" class="form-control" id="subject" name="subject" value="{{.subject}}"
-                            placeholder="例: 数学、英語、情報">
+                        <input type="text" class="form-control" id="subject" name="subject" value="{{.subject}}" placeholder="例: 数学、英語、情報">
                     </div>
                     <div class="mb-3">
                         <label for="priority" class="form-label">重要度</label>
                         <select class="form-select" id="priority" name="priority">
-                            <option value="low" {{if eq .priority "low" }}selected{{end}}>小</option>
-                            <option value="medium" {{if not (or (eq .priority "low" ) (eq .priority "high"
-                                ))}}selected{{end}}>中</option>
-                            <option value="high" {{if eq .priority "high" }}selected{{end}}>大</option>
+                            <option value="low"    {{if eq .priority "low"   }}selected{{end}}>低</option>
+                            <option value="medium" {{if not (or (eq .priority "low") (eq .priority "high"))}}selected{{end}}>中</option>
+                            <option value="high"   {{if eq .priority "high"  }}selected{{end}}>高</option>
                         </select>
                     </div>
                     <div class="mb-3">
-                        <label for="due_date" class="form-label">提出期限 <span class="text-danger">*</span></label>
-                        <input type="datetime-local" class="form-control" id="due_date" name="due_date" required>
+                        <label for="due_date" class="form-label">提出期限 <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
+                        <input type="datetime-local" class="form-control" id="due_date" name="due_date" value="{{.defaultDueDate}}" required>
                     </div>
                     <div class="mb-3">
                         <label for="description" class="form-label">説明</label>
-                        <textarea class="form-control" id="description" name="description"
-                            rows="3">{{.description}}</textarea>
+                        <textarea class="form-control" id="description" name="description" rows="3">{{.description}}</textarea>
                     </div>
-                    <!-- 通知設定 -->
                     <div class="card bg-light mb-3">
                         <div class="card-body py-2">
-                            <h6 class="mb-2"><i class="bi bi-bell me-1"></i>通知設定</h6>
-                            <!-- 督促通知 -->
+                            <h6 class="mb-2"><i class="bi bi-bell me-1" aria-hidden="true"></i>通知設定</h6>
                             <div class="form-check form-switch mb-2">
-                                <input class="form-check-input" type="checkbox" id="urgent_reminder_enabled"
-                                    name="urgent_reminder_enabled" checked>
+                                <input class="form-check-input" type="checkbox" id="urgent_reminder_enabled" name="urgent_reminder_enabled" checked>
                                 <label class="form-check-label" for="urgent_reminder_enabled">
                                     督促通知（期限3時間前から繰り返し通知）
                                 </label>
                             </div>
                             <div class="form-text small mb-2">
-                                重要度により間隔が変わります：大=10分、中=30分、小=1時間
+                                重要度により通知間隔が変わります：高=10分ごと、中=30分ごと、低=1時間ごと
                             </div>
                             <hr class="my-2">
                             <div class="form-check form-switch">
-                                <input class="form-check-input" type="checkbox" id="reminder_enabled"
-                                    name="reminder_enabled" onchange="toggleReminderDate(this)">
+                                <input class="form-check-input" type="checkbox" id="reminder_enabled" name="reminder_enabled" onchange="toggleReminderDate(this)">
                                 <label class="form-check-label" for="reminder_enabled">
                                     リマインダー（指定日時に通知）
                                 </label>
                             </div>
                             <div class="mt-2" id="reminder_at_group" style="display: none;">
                                 <label for="reminder_at" class="form-label small">通知日時</label>
-                                <input type="datetime-local" class="form-control form-control-sm" id="reminder_at"
-                                    name="reminder_at">
+                                <input type="datetime-local" class="form-control form-control-sm" id="reminder_at" name="reminder_at">
                             </div>
                         </div>
                     </div>
                     <div class="card bg-light mb-3">
-                        <div class="card-header py-2" style="cursor: pointer;" data-bs-toggle="collapse"
-                            data-bs-target="#recurringSettings">
-                            <h6 class="mb-0"><i class="bi bi-arrow-repeat me-1"></i>繰り返し設定 <i
-                                    class="bi bi-chevron-down float-end"></i></h6>
+                        <div class="card-header py-2" style="cursor: pointer;" data-bs-toggle="collapse" data-bs-target="#recurringSettings" aria-expanded="false" aria-controls="recurringSettings">
+                            <h6 class="mb-0"><i class="bi bi-arrow-repeat me-1" aria-hidden="true"></i>繰り返し設定 <i class="bi bi-chevron-down float-end" aria-hidden="true"></i></h6>
                         </div>
                         <div class="collapse" id="recurringSettings">
                             <div class="card-body py-2">
                                 <div class="row mb-2">
                                     <div class="col-6">
                                         <label for="recurrence_type" class="form-label small">繰り返しタイプ</label>
-                                        <select class="form-select form-select-sm" id="recurrence_type"
-                                            name="recurrence_type" onchange="updateRecurrenceOptions()">
+                                        <select class="form-select form-select-sm" id="recurrence_type" name="recurrence_type" onchange="updateRecurrenceOptions()">
                                             <option value="none" selected>なし</option>
                                             <option value="daily">毎日</option>
                                             <option value="weekly">毎週</option>
@@ -91,107 +79,130 @@
                                     <div class="col-6" id="interval_group" style="display: none;">
                                         <label for="recurrence_interval" class="form-label small">間隔</label>
                                         <div class="input-group input-group-sm">
-                                            <input type="number" class="form-control" id="recurrence_interval"
-                                                name="recurrence_interval" value="1" min="1" max="12">
+                                            <input type="number" class="form-control" id="recurrence_interval" name="recurrence_interval" value="1" min="1" max="12" onchange="updateLeadDaysMax()">
                                             <span class="input-group-text" id="interval_label">週</span>
                                         </div>
                                     </div>
                                 </div>
-                                <div id="weekday_group" style="display: none;" class="mb-2">
+                                <div id="weekday_group" class="mb-2">
                                     <label class="form-label small">曜日</label>
-                                    <div class="btn-group btn-group-sm w-100" role="group">
-                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd0"
-                                            value="0" {{if eq .currentWeekday 0}}checked{{end}}>
+                                    <div class="btn-group btn-group-sm w-100" role="group" aria-label="曜日選択">
+                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd0" value="0" {{if eq .currentWeekday 0}}checked{{end}}>
                                         <label class="btn btn-outline-primary" for="wd0">日</label>
-                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd1"
-                                            value="1" {{if eq .currentWeekday 1}}checked{{end}}>
+                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd1" value="1" {{if eq .currentWeekday 1}}checked{{end}}>
                                         <label class="btn btn-outline-primary" for="wd1">月</label>
-                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd2"
-                                            value="2" {{if eq .currentWeekday 2}}checked{{end}}>
+                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd2" value="2" {{if eq .currentWeekday 2}}checked{{end}}>
                                         <label class="btn btn-outline-primary" for="wd2">火</label>
-                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd3"
-                                            value="3" {{if eq .currentWeekday 3}}checked{{end}}>
+                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd3" value="3" {{if eq .currentWeekday 3}}checked{{end}}>
                                         <label class="btn btn-outline-primary" for="wd3">水</label>
-                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd4"
-                                            value="4" {{if eq .currentWeekday 4}}checked{{end}}>
+                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd4" value="4" {{if eq .currentWeekday 4}}checked{{end}}>
                                         <label class="btn btn-outline-primary" for="wd4">木</label>
-                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd5"
-                                            value="5" {{if eq .currentWeekday 5}}checked{{end}}>
+                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd5" value="5" {{if eq .currentWeekday 5}}checked{{end}}>
                                         <label class="btn btn-outline-primary" for="wd5">金</label>
-                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd6"
-                                            value="6" {{if eq .currentWeekday 6}}checked{{end}}>
+                                        <input type="radio" class="btn-check" name="recurrence_weekday" id="wd6" value="6" {{if eq .currentWeekday 6}}checked{{end}}>
                                         <label class="btn btn-outline-primary" for="wd6">土</label>
                                     </div>
                                 </div>
-                                <div id="day_group" style="display: none;" class="mb-2">
+                                <div id="day_group" class="mb-2">
                                     <label for="recurrence_day" class="form-label small">日</label>
-                                    <select class="form-select form-select-sm" id="recurrence_day"
-                                        name="recurrence_day">
+                                    <select class="form-select form-select-sm" id="recurrence_day" name="recurrence_day">
                                         {{range $i := seq 1 31}}
                                         <option value="{{$i}}" {{if eq $.currentDay $i}}selected{{end}}>{{$i}}日</option>
                                         {{end}}
                                     </select>
                                 </div>
+                                <div id="lead_days_group" style="display: none;" class="mb-2">
+                                    <label class="form-label small">リストに追加するタイミング</label>
+                                    <div class="d-flex align-items-center gap-2">
+                                        <div class="input-group input-group-sm" style="width: 120px;">
+                                            <input type="number" class="form-control" id="generation_lead_days" name="generation_lead_days" value="0" min="0" max="0">
+                                            <span class="input-group-text">日前</span>
+                                        </div>
+                                        <input type="time" class="form-control form-control-sm" id="generation_lead_time" name="generation_lead_time" style="width: 110px;">
+                                    </div>
+                                    <div class="form-text small text-muted" id="lead_days_hint"></div>
+                                </div>
                                 <div id="end_group" style="display: none;">
                                     <label class="form-label small">終了条件</label>
                                     <div class="form-check form-check-inline">
-                                        <input class="form-check-input" type="radio" name="end_type" id="end_never"
-                                            value="never" checked>
+                                        <input class="form-check-input" type="radio" name="end_type" id="end_never" value="never" checked>
                                         <label class="form-check-label small" for="end_never">無期限</label>
                                     </div>
                                     <div class="form-check form-check-inline">
-                                        <input class="form-check-input" type="radio" name="end_type" id="end_count"
-                                            value="count">
+                                        <input class="form-check-input" type="radio" name="end_type" id="end_count" value="count">
                                         <label class="form-check-label small" for="end_count">回数</label>
                                     </div>
                                     <div class="form-check form-check-inline">
-                                        <input class="form-check-input" type="radio" name="end_type" id="end_date"
-                                            value="date">
+                                        <input class="form-check-input" type="radio" name="end_type" id="end_date" value="date">
                                         <label class="form-check-label small" for="end_date">終了日</label>
                                     </div>
                                     <div class="mt-1" id="end_count_group" style="display: none;">
-                                        <input type="number" class="form-control form-control-sm" id="end_count_value"
-                                            name="end_count" value="10" min="1" style="width: 100px;">
+                                        <input type="number" class="form-control form-control-sm" id="end_count_value" name="end_count" value="10" min="1" style="width: 100px;">
                                     </div>
                                     <div class="mt-1" id="end_date_group" style="display: none;">
-                                        <input type="date" class="form-control form-control-sm" id="end_date_value"
-                                            name="end_date" style="width: 150px;">
+                                        <input type="date" class="form-control form-control-sm" id="end_date_value" name="end_date" style="width: 150px;">
                                     </div>
                                 </div>
                             </div>
                         </div>
                     </div>
+                    <div class="d-flex gap-2">
+                        <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1" aria-hidden="true"></i>登録</button>
+                        <a href="/assignments" class="btn btn-outline-secondary">キャンセル</a>
+                    </div>
+                </form>
             </div>
-            <div class="d-flex gap-2">
-                <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1"></i>登録</button>
-                <a href="/assignments" class="btn btn-outline-secondary">キャンセル</a>
-            </div>
-            </form>
         </div>
     </div>
 </div>
-</div>
 <script>
     function toggleReminderDate(checkbox) {
         document.getElementById('reminder_at_group').style.display = checkbox.checked ? 'block' : 'none';
     }
+    function getLeadDaysMax() {
+        const type = document.getElementById('recurrence_type').value;
+        const interval = parseInt(document.getElementById('recurrence_interval').value) || 1;
+        if (type === 'daily') return interval;
+        if (type === 'weekly') return interval * 7;
+        if (type === 'monthly') return interval * 28;
+        return 0;
+    }
+    function updateLeadDaysMax() {
+        const max = getLeadDaysMax();
+        const input = document.getElementById('generation_lead_days');
+        input.max = max;
+        if (parseInt(input.value) > max) input.value = max;
+        const type = document.getElementById('recurrence_type').value;
+        const labels = { daily: '日', weekly: '週', monthly: 'ヶ月' };
+        const interval = document.getElementById('recurrence_interval').value;
+        document.getElementById('lead_days_hint').textContent =
+            max === 0 ? '間隔が1日のため、事前追加は設定できません' :
+            `最大${max}日前まで指定可能（繰り返し間隔${interval}${labels[type]}以内）`;
+    }
     function updateRecurrenceOptions() {
         const type = document.getElementById('recurrence_type').value;
         const isRecurring = type !== 'none';
         document.getElementById('interval_group').style.display = isRecurring ? 'block' : 'none';
         document.getElementById('weekday_group').style.display = type === 'weekly' ? 'block' : 'none';
         document.getElementById('day_group').style.display = type === 'monthly' ? 'block' : 'none';
+        document.getElementById('lead_days_group').style.display = isRecurring ? 'block' : 'none';
         document.getElementById('end_group').style.display = isRecurring ? 'block' : 'none';
         const label = document.getElementById('interval_label');
-        if (type === 'daily') label.textContent = '日';
-        else if (type === 'weekly') label.textContent = '週';
-        else if (type === 'monthly') label.textContent = '月';
+        if (label) {
+            if (type === 'daily') label.textContent = '日';
+            else if (type === 'weekly') label.textContent = '週';
+            else if (type === 'monthly') label.textContent = '月';
+        }
+        updateLeadDaysMax();
     }
-    document.querySelectorAll('input[name="end_type"]').forEach(radio => {
+    document.querySelectorAll('input[name="end_type"]').forEach(function(radio) {
         radio.addEventListener('change', function () {
             document.getElementById('end_count_group').style.display = this.value === 'count' ? 'block' : 'none';
             document.getElementById('end_date_group').style.display = this.value === 'date' ? 'block' : 'none';
         });
     });
+    document.getElementById('recurringSettings').addEventListener('show.bs.collapse', function () {
+        updateLeadDaysMax();
+    });
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/assignments/statistics.html b/web/templates/assignments/statistics.html
index 9056744..1d97acd 100644
--- a/web/templates/assignments/statistics.html
+++ b/web/templates/assignments/statistics.html
@@ -2,111 +2,43 @@
 
 {{define "head"}}
 <style>
-    .stat-card {
-        transition: transform 0.2s ease-in-out;
-    }
-
-    .stat-card:hover {
-        transform: translateY(-5px);
-    }
-
-    .progress {
-        height: 25px;
-    }
-
-    .progress-bar {
-        font-size: 0.9rem;
-        font-weight: 500;
-    }
-
-    .subject-row:hover {
-        background-color: rgba(0, 0, 0, 0.02);
-    }
-
-    .table-progress {
-        height: 20px;
-    }
-
-    .pagination-info {
-        font-size: 0.875rem;
-    }
-
-    .stats-table {
-        min-width: 700px;
-    }
-
-    .stats-table th,
-    .stats-table td {
-        white-space: nowrap;
-    }
-
-    .stats-table th:first-child,
-    .stats-table td:first-child {
-        min-width: 120px;
-    }
-
+    .stat-card { transition: transform 0.2s ease-in-out; }
+    .stat-card:hover { transform: translateY(-5px); }
+    .progress { height: 25px; }
+    .progress-bar { font-size: 0.9rem; font-weight: 500; }
+    .subject-row:hover { background-color: rgba(0, 0, 0, 0.02); }
+    .table-progress { height: 20px; }
+    .pagination-info { font-size: 0.875rem; }
+    .stats-table { min-width: 700px; }
+    .stats-table th, .stats-table td { white-space: nowrap; }
+    .stats-table th:first-child, .stats-table td:first-child { min-width: 120px; }
     #shareCard {
-        width: 600px;
-        height: 315px;
-        position: fixed;
-        left: -9999px;
-        top: 0;
+        width: 600px; height: 315px;
+        position: fixed; left: -9999px; top: 0;
         background: linear-gradient(135deg, #005bea 0%, #00c6fb 100%);
-        padding: 2rem;
-        color: white;
-        border-radius: 12px;
-        display: flex;
-        flex-direction: column;
-        justify-content: space-between;
+        padding: 2rem; color: white; border-radius: 12px;
+        display: flex; flex-direction: column; justify-content: space-between;
         font-family: 'Inter', system-ui, -apple-system, sans-serif;
     }
-
-    #shareCard .card-title {
-        font-size: 1.5rem;
-        font-weight: bold;
-        opacity: 0.9;
-    }
-
-    #shareCard .rate-display {
-        font-size: 5rem;
-        font-weight: bold;
-        line-height: 1;
-        margin: 1rem 0;
-    }
-
+    #shareCard .card-title { font-size: 1.5rem; font-weight: bold; opacity: 0.9; }
+    #shareCard .rate-display { font-size: 5rem; font-weight: bold; line-height: 1; margin: 1rem 0; }
     #shareCard .stats-row {
-        display: flex;
-        justify-content: space-around;
-        background: rgba(255, 255, 255, 0.1);
-        border-radius: 8px;
-        padding: 1rem;
+        display: flex; justify-content: space-around;
+        background: rgba(255,255,255,0.1); border-radius: 8px; padding: 1rem;
         backdrop-filter: blur(5px);
     }
-
-    #shareCard .stat-item {
-        text-align: center;
-    }
-
-    #shareCard .stat-label {
-        font-size: 0.8rem;
-        opacity: 0.8;
-        display: block;
-        margin-bottom: 0.2rem;
-    }
-
-    #shareCard .stat-value {
-        font-size: 1.4rem;
-        font-weight: bold;
-    }
+    #shareCard .stat-item { text-align: center; }
+    #shareCard .stat-label { font-size: 0.8rem; opacity: 0.8; display: block; margin-bottom: 0.2rem; }
+    #shareCard .stat-value { font-size: 1.4rem; font-weight: bold; }
 </style>
 <script src="https://cdn.jsdelivr.net/npm/html2canvas@1.4.1/dist/html2canvas.min.js"></script>
 {{end}}
 
 {{define "content"}}
 <div class="d-flex justify-content-between align-items-center mb-4">
-    <h1><i class="bi bi-bar-chart me-2"></i>統計</h1>
+    <h1><i class="bi bi-bar-chart me-2" aria-hidden="true"></i>統計</h1>
     <a href="/assignments" class="btn btn-outline-secondary">
-        <i class="bi bi-arrow-left me-1"></i>課題一覧に戻る
+        <i class="bi bi-arrow-left me-1" aria-hidden="true"></i>課題一覧に戻る
     </a>
 </div>
 
@@ -114,35 +46,67 @@
     <div class="card-body">
         <form method="GET" action="/statistics" class="row g-3">
             <div class="col-md-4">
-                <label class="form-label">科目</label>
-                <select name="subject" class="form-select">
+                <label for="subjectFilter" class="form-label">科目</label>
+                <select id="subjectFilter" name="subject" class="form-select">
                     <option value="">すべての科目</option>
                     {{range .subjects}}
-                    <option value="{{.}}" {{if eq . $.selectedSubject}}selected{{end}}>{{.}}{{if index
-                        $.archivedSubjects .}} (アーカイブ済){{end}}</option>
+                    <option value="{{.}}" {{if eq . $.selectedSubject}}selected{{end}}>{{.}}{{if index $.archivedSubjects .}} (アーカイブ済){{end}}</option>
                     {{end}}
                 </select>
             </div>
             <div class="col-md-2">
-                <label class="form-label">登録日（開始）</label>
-                <input type="date" name="from" class="form-control" value="{{.fromDate}}">
+                <label for="fromDate" class="form-label">登録日（開始）</label>
+                <input type="date" id="fromDate" name="from" class="form-control" value="{{.fromDate}}">
             </div>
             <div class="col-md-2">
-                <label class="form-label">登録日（終了）</label>
-                <input type="date" name="to" class="form-control" value="{{.toDate}}">
+                <label for="toDate" class="form-label">登録日（終了）</label>
+                <input type="date" id="toDate" name="to" class="form-control" value="{{.toDate}}">
             </div>
             <div class="col-md-4 d-flex align-items-end">
                 <button type="submit" class="btn btn-primary me-2">
-                    <i class="bi bi-filter me-1"></i>絞り込み
+                    <i class="bi bi-filter me-1" aria-hidden="true"></i>絞り込み
                 </button>
                 <a href="/statistics" class="btn btn-outline-secondary">
-                    <i class="bi bi-x-lg me-1"></i>リセット
+                    <i class="bi bi-x-lg me-1" aria-hidden="true"></i>リセット
                 </a>
             </div>
         </form>
     </div>
 </div>
 
+<div class="card mb-4">
+    <div class="card-header">
+        <i class="bi bi-download me-2" aria-hidden="true"></i>CSVエクスポート
+    </div>
+    <div class="card-body">
+        <form method="GET" action="/assignments/export" class="row g-3">
+            <div class="col-md-3">
+                <label for="csvSubject" class="form-label">科目</label>
+                <select id="csvSubject" name="subject" class="form-select">
+                    <option value="">すべての科目</option>
+                    {{range .subjects}}
+                    <option value="{{.}}">{{.}}</option>
+                    {{end}}
+                </select>
+            </div>
+            <div class="col-md-3">
+                <label for="csvFrom" class="form-label">提出期限（開始）</label>
+                <input type="date" id="csvFrom" name="from" class="form-control">
+            </div>
+            <div class="col-md-3">
+                <label for="csvTo" class="form-label">提出期限（終了）</label>
+                <input type="date" id="csvTo" name="to" class="form-control">
+            </div>
+            <div class="col-md-3 d-flex align-items-end">
+                <button type="submit" class="btn btn-outline-secondary">
+                    <i class="bi bi-file-earmark-spreadsheet me-1" aria-hidden="true"></i>CSVダウンロード
+                </button>
+            </div>
+        </form>
+        <small class="text-muted mt-2 d-block">期間・科目を指定しない場合は全件をエクスポートします。提出期限を基準に絞り込みます。</small>
+    </div>
+</div>
+
 <div class="row g-4 mb-4">
     <div class="col-6 col-lg-3">
         <div class="card stat-card bg-primary text-white h-100">
@@ -152,7 +116,7 @@
                         <h6 class="text-white-50 mb-1">総課題数</h6>
                         <h2 class="mb-0">{{.stats.TotalAssignments}}</h2>
                     </div>
-                    <i class="bi bi-list-task display-4 opacity-50"></i>
+                    <i class="bi bi-list-task display-4 opacity-50" aria-hidden="true"></i>
                 </div>
             </div>
         </div>
@@ -165,7 +129,7 @@
                         <h6 class="text-white-50 mb-1">完了</h6>
                         <h2 class="mb-0">{{.stats.CompletedAssignments}}</h2>
                     </div>
-                    <i class="bi bi-check-circle display-4 opacity-50"></i>
+                    <i class="bi bi-check-circle display-4 opacity-50" aria-hidden="true"></i>
                 </div>
             </div>
         </div>
@@ -178,7 +142,7 @@
                         <h6 class="text-dark-50 mb-1">未完了</h6>
                         <h2 class="mb-0">{{.stats.PendingAssignments}}</h2>
                     </div>
-                    <i class="bi bi-hourglass-split display-4 opacity-50"></i>
+                    <i class="bi bi-hourglass-split display-4 opacity-50" aria-hidden="true"></i>
                 </div>
             </div>
         </div>
@@ -191,7 +155,7 @@
                         <h6 class="text-white-50 mb-1">期限切れ</h6>
                         <h2 class="mb-0">{{.stats.OverdueAssignments}}</h2>
                     </div>
-                    <i class="bi bi-exclamation-triangle display-4 opacity-50"></i>
+                    <i class="bi bi-exclamation-triangle display-4 opacity-50" aria-hidden="true"></i>
                 </div>
             </div>
         </div>
@@ -200,38 +164,24 @@
 
 <div class="card mb-4">
     <div class="card-header d-flex justify-content-between align-items-center">
-        <span><i class="bi bi-clock-history me-2"></i>期限内完了率</span>
+        <span><i class="bi bi-clock-history me-2" aria-hidden="true"></i>期限内完了率</span>
         <button class="btn btn-sm btn-outline-primary" onclick="generateShareImage()">
-            <i class="bi bi-share me-1"></i>シェア
+            <i class="bi bi-share me-1" aria-hidden="true"></i>シェア
         </button>
     </div>
     <div class="card-body">
         <div class="row align-items-center">
             <div class="col-md-3 text-center mb-3 mb-md-0">
-                <h1
-                    class="display-3 mb-0 {{if ge .stats.OnTimeCompletionRate 80.0}}text-success{{else if ge .stats.OnTimeCompletionRate 50.0}}text-warning{{else}}text-danger{{end}}">
+                <p class="display-3 mb-0 {{if ge .stats.OnTimeCompletionRate 80.0}}text-success{{else if ge .stats.OnTimeCompletionRate 50.0}}text-warning{{else}}text-danger{{end}}" aria-label="期限内完了率 {{printf "%.1f" .stats.OnTimeCompletionRate}}パーセント">
                     {{printf "%.1f" .stats.OnTimeCompletionRate}}%
-                </h1>
+                </p>
                 <small class="text-muted">期限内完了率</small>
             </div>
             <div class="col-md-9">
-                <div class="progress">
-                    {{if ge .stats.OnTimeCompletionRate 80.0}}
-                    <div class="progress-bar bg-success" role="progressbar"
-                        style="width: {{.stats.OnTimeCompletionRate}}%">
+                <div class="progress" role="progressbar" aria-label="期限内完了率" aria-valuenow="{{printf "%.0f" .stats.OnTimeCompletionRate}}" aria-valuemin="0" aria-valuemax="100">
+                    <div class="progress-bar {{if ge .stats.OnTimeCompletionRate 80.0}}bg-success{{else if ge .stats.OnTimeCompletionRate 50.0}}bg-warning{{else}}bg-danger{{end}}" style="width: {{.stats.OnTimeCompletionRate}}%">
                         {{printf "%.1f" .stats.OnTimeCompletionRate}}% 期限内に完了
                     </div>
-                    {{else if ge .stats.OnTimeCompletionRate 50.0}}
-                    <div class="progress-bar bg-warning" role="progressbar"
-                        style="width: {{.stats.OnTimeCompletionRate}}%">
-                        {{printf "%.1f" .stats.OnTimeCompletionRate}}% 期限内に完了
-                    </div>
-                    {{else}}
-                    <div class="progress-bar bg-danger" role="progressbar"
-                        style="width: {{.stats.OnTimeCompletionRate}}%">
-                        {{printf "%.1f" .stats.OnTimeCompletionRate}}% 期限内に完了
-                    </div>
-                    {{end}}
                 </div>
                 <small class="text-muted mt-2 d-block">完了した課題のうち、期限内に完了した割合を表示しています。</small>
             </div>
@@ -241,22 +191,22 @@
 
 <div class="card mb-4" id="activeSubjectsCard">
     <div class="card-header d-flex justify-content-between align-items-center">
-        <span><i class="bi bi-collection me-2"></i>アクティブ科目</span>
+        <span><i class="bi bi-collection me-2" aria-hidden="true"></i>アクティブ科目</span>
         <span class="badge bg-primary" id="activeCount">0</span>
     </div>
     <div class="card-body p-0">
         <div class="table-responsive">
-            <table class="table table-hover mb-0 stats-table">
+            <table class="table table-hover mb-0 stats-table" aria-label="アクティブ科目統計">
                 <thead class="table-light">
                     <tr>
-                        <th>科目</th>
-                        <th class="text-center">総数</th>
-                        <th class="text-center">完了</th>
-                        <th class="text-center">未完了</th>
-                        <th class="text-center">期限切れ</th>
-                        <th class="text-center">完了率</th>
-                        <th style="width: 150px;">進捗</th>
-                        <th class="text-center">操作</th>
+                        <th scope="col">科目</th>
+                        <th scope="col" class="text-center">総数</th>
+                        <th scope="col" class="text-center">完了</th>
+                        <th scope="col" class="text-center">未完了</th>
+                        <th scope="col" class="text-center">期限切れ</th>
+                        <th scope="col" class="text-center">完了率</th>
+                        <th scope="col" style="width: 150px;">進捗</th>
+                        <th scope="col" class="text-center">操作</th>
                     </tr>
                 </thead>
                 <tbody id="activeSubjectsBody"></tbody>
@@ -265,7 +215,7 @@
     </div>
     <div class="card-footer d-flex justify-content-between align-items-center">
         <span class="pagination-info" id="activePageInfo"></span>
-        <nav>
+        <nav aria-label="アクティブ科目ページナビゲーション">
             <ul class="pagination pagination-sm mb-0" id="activePagination"></ul>
         </nav>
     </div>
@@ -273,22 +223,22 @@
 
 <div class="card" id="archivedSubjectsCard">
     <div class="card-header d-flex justify-content-between align-items-center">
-        <span><i class="bi bi-archive me-2"></i>アーカイブ済み科目</span>
+        <span><i class="bi bi-archive me-2" aria-hidden="true"></i>アーカイブ済み科目</span>
         <span class="badge bg-secondary" id="archivedCount">0</span>
     </div>
     <div class="card-body p-0">
         <div class="table-responsive">
-            <table class="table table-hover mb-0 stats-table">
+            <table class="table table-hover mb-0 stats-table" aria-label="アーカイブ済み科目統計">
                 <thead class="table-light">
                     <tr>
-                        <th>科目</th>
-                        <th class="text-center">総数</th>
-                        <th class="text-center">完了</th>
-                        <th class="text-center">未完了</th>
-                        <th class="text-center">期限切れ</th>
-                        <th class="text-center">完了率</th>
-                        <th style="width: 150px;">進捗</th>
-                        <th class="text-center">操作</th>
+                        <th scope="col">科目</th>
+                        <th scope="col" class="text-center">総数</th>
+                        <th scope="col" class="text-center">完了</th>
+                        <th scope="col" class="text-center">未完了</th>
+                        <th scope="col" class="text-center">期限切れ</th>
+                        <th scope="col" class="text-center">完了率</th>
+                        <th scope="col" style="width: 150px;">進捗</th>
+                        <th scope="col" class="text-center">操作</th>
                     </tr>
                 </thead>
                 <tbody id="archivedSubjectsBody"></tbody>
@@ -297,7 +247,7 @@
     </div>
     <div class="card-footer d-flex justify-content-between align-items-center">
         <span class="pagination-info" id="archivedPageInfo"></span>
-        <nav>
+        <nav aria-label="アーカイブ済み科目ページナビゲーション">
             <ul class="pagination pagination-sm mb-0" id="archivedPagination"></ul>
         </nav>
     </div>
@@ -305,27 +255,25 @@
 
 <div class="card d-none" id="noSubjectsCard">
     <div class="card-body text-center py-5">
-        <i class="bi bi-inbox display-1 text-muted"></i>
+        <i class="bi bi-inbox display-1 text-muted" aria-hidden="true"></i>
         <h4 class="mt-3">科目別の統計データがありません</h4>
         <p class="text-muted">課題を登録して科目を設定すると、ここに統計が表示されます。</p>
     </div>
 </div>
 
-<div id="shareCard">
+<div id="shareCard" aria-hidden="true">
     <div>
         <div class="d-flex align-items-center mb-4">
             <i class="bi bi-journal-check me-2" style="font-size: 1.5rem;"></i>
             <span class="card-title">Super Homework Manager</span>
         </div>
     </div>
-
     <div class="text-center">
         <div style="font-size: 1.5rem; font-weight: bold; margin-bottom: 0.5rem; opacity: 0.9;">期限内完了率</div>
         <div class="rate-display" style="margin-top: 0;">
             {{printf "%.1f" .stats.OnTimeCompletionRate}}<span style="font-size: 2.5rem;">%</span>
         </div>
     </div>
-
     <div class="stats-row">
         <div class="stat-item">
             <span class="stat-label">完了</span>
@@ -342,31 +290,28 @@
     </div>
 </div>
 
-<!-- Share Modal -->
-<div class="modal fade" id="shareModal" tabindex="-1">
+<div class="modal fade" id="shareModal" tabindex="-1" aria-labelledby="shareModalHeading" aria-modal="true" role="dialog">
     <div class="modal-dialog modal-dialog-centered">
         <div class="modal-content">
             <div class="modal-header">
-                <h5 class="modal-title"><i class="bi bi-share me-2"></i>シェア</h5>
-                <button type="button" class="btn-close" data-bs-dismiss="modal"></button>
+                <h5 class="modal-title" id="shareModalHeading"><i class="bi bi-share me-2" aria-hidden="true"></i>シェア</h5>
+                <button type="button" class="btn-close" data-bs-dismiss="modal" aria-label="閉じる"></button>
             </div>
             <div class="modal-body text-center">
-                <div id="sharePreviewContainer" class="mb-3" style="max-width: 100%; overflow: hidden;">
-                </div>
+                <div id="sharePreviewContainer" class="mb-3" style="max-width: 100%; overflow: hidden;"></div>
                 <p class="text-muted small mb-3">
                     画像を保存またはコピーして、SNSに貼り付けてください。<br>
-                    <span class="text-danger"><i class="bi bi-info-circle me-1"></i>ブラウザの制限により、自動で画像は添付されません。</span>
+                    <span class="text-danger"><i class="bi bi-info-circle me-1" aria-hidden="true"></i>ブラウザの制限により、自動で画像は添付されません。</span>
                 </p>
                 <div class="d-grid gap-2">
-                    <button class="btn btn-outline-primary" onclick="copyImageToClipboard(this)">
-                        <i class="bi bi-clipboard me-2"></i>画像をコピー
+                    <button class="btn btn-outline-primary" id="copyImageBtn">
+                        <i class="bi bi-clipboard me-2" aria-hidden="true"></i>画像をコピー
                     </button>
                     <a id="downloadLink" class="btn btn-outline-secondary" download="stats.png">
-                        <i class="bi bi-download me-2"></i>画像を保存
+                        <i class="bi bi-download me-2" aria-hidden="true"></i>画像を保存
                     </a>
-                    <a id="twitterShareBtn" href="#" target="_blank" class="btn btn-dark"
-                        style="background-color: #000;">
-                        <i class="bi bi-twitter-x me-2"></i>Xでポストする
+                    <a id="twitterShareBtn" href="#" target="_blank" rel="noopener noreferrer" class="btn btn-dark" style="background-color: #000;">
+                        <i class="bi bi-twitter-x me-2" aria-hidden="true"></i>Xでポストする
                     </a>
                 </div>
             </div>
@@ -381,28 +326,23 @@
 </script>
 <script>
     (function () {
-        var data = JSON.parse(document.getElementById('subjectsData').textContent);
-        var csrfToken = data.csrfToken;
-        var subjects = data.subjects;
-        var PAGE_SIZE = 10;
-        var activeSubjects = subjects.filter(function (s) { return !s.isArchived; });
+        var data            = JSON.parse(document.getElementById('subjectsData').textContent);
+        var csrfToken       = data.csrfToken;
+        var subjects        = data.subjects;
+        var PAGE_SIZE       = 10;
+        var activeSubjects  = subjects.filter(function (s) { return !s.isArchived; });
         var archivedSubjects = subjects.filter(function (s) { return s.isArchived; });
-        var activePage = 1;
-        var archivedPage = 1;
+        var activePage      = 1;
+        var archivedPage    = 1;
+        var _capturedCanvas = null;
 
-        // Share Functionality
         window.generateShareImage = function () {
             var card = document.getElementById('shareCard');
-            // Ensure card is visible for rendering but off-screen
             card.style.display = 'flex';
-
-            html2canvas(card, {
-                backgroundColor: null,
-                scale: 2 // High resolution
-            }).then(canvas => {
+            html2canvas(card, { backgroundColor: null, scale: 2 }).then(function(canvas) {
+                _capturedCanvas = canvas;
                 var imgData = canvas.toDataURL('image/png');
 
-                // Set up preview
                 var previewContainer = document.getElementById('sharePreviewContainer');
                 previewContainer.innerHTML = '';
                 var img = document.createElement('img');
@@ -410,67 +350,51 @@
                 img.style.maxWidth = '100%';
                 img.style.borderRadius = '8px';
                 img.style.boxShadow = '0 4px 12px rgba(0,0,0,0.1)';
+                img.alt = '統計シェア画像';
                 previewContainer.appendChild(img);
 
-                // Set up download link
-                var downloadLink = document.getElementById('downloadLink');
-                downloadLink.href = imgData;
+                document.getElementById('downloadLink').href = imgData;
 
-                // Set up Twitter button
                 var text = '私の課題完了状況\n期限内完了率: {{printf "%.1f" .stats.OnTimeCompletionRate}}%\n#SuperHomeworkManager';
-                var twitterBtn = document.getElementById('twitterShareBtn');
-                twitterBtn.href = "https://twitter.com/intent/tweet?text=" + encodeURIComponent(text);
+                document.getElementById('twitterShareBtn').href = 'https://twitter.com/intent/tweet?text=' + encodeURIComponent(text);
 
-                // Show modal
-                var modal = new bootstrap.Modal(document.getElementById('shareModal'));
-                modal.show();
+                new bootstrap.Modal(document.getElementById('shareModal')).show();
             });
         };
 
-        // Helper to convert Data URL to Blob
         function dataURLtoBlob(dataurl) {
-            var arr = dataurl.split(','), mime = arr[0].match(/:(.*?);/)[1],
-                bstr = atob(arr[1]), n = bstr.length, u8arr = new Uint8Array(n);
-            while (n--) {
-                u8arr[n] = bstr.charCodeAt(n);
-            }
-            return new Blob([u8arr], { type: mime });
+            var arr  = dataurl.split(',');
+            var mime = arr[0].match(/:(.*?);/)[1];
+            var bstr = atob(arr[1]);
+            var n    = bstr.length;
+            var u8   = new Uint8Array(n);
+            while (n--) u8[n] = bstr.charCodeAt(n);
+            return new Blob([u8], { type: mime });
         }
 
-        window.copyImageToClipboard = function (btn) {
-            var canvas = document.querySelector('#sharePreviewContainer img');
-            if (!canvas) return;
+        document.getElementById('copyImageBtn').addEventListener('click', function() {
+            var btn = this;
+            var imgEl = document.querySelector('#sharePreviewContainer img');
+            if (!imgEl) return;
 
-            if (!navigator.clipboard) {
-                alert('このブラウザまたは環境（非HTTPS/非localhost）では、クリップボードへのコピー機能がサポートされていません。\n「画像を保存」を使用してください。');
+            if (!navigator.clipboard || !window.ClipboardItem) {
+                showCopyFeedback('このブラウザではクリップボードへの画像コピーがサポートされていません。「画像を保存」をご利用ください。');
                 return;
             }
 
-            try {
-                var blob = dataURLtoBlob(canvas.src);
-                navigator.clipboard.write([
-                    new ClipboardItem({
-                        'image/png': blob
-                    })
-                ]).then(function () {
-                    var originalText = btn.innerHTML;
-                    btn.innerHTML = '<i class="bi bi-check me-2"></i>コピーしました';
-                    btn.classList.remove('btn-outline-primary');
-                    btn.classList.add('btn-success');
-                    setTimeout(function () {
-                        btn.innerHTML = originalText;
-                        btn.classList.add('btn-outline-primary');
-                        btn.classList.remove('btn-success');
-                    }, 2000);
-                }).catch(function (err) {
-                    console.error('Failed to copy: ', err);
-                    alert('画像のコピーに失敗しました。\nエラー: ' + err.message + '\n「画像を保存」を使用してください。');
-                });
-            } catch (err) {
-                console.error('Failed to create blob: ', err);
-                alert('画像データの生成に失敗しました: ' + err.message);
-            }
-        };
+            var blob = dataURLtoBlob(imgEl.src);
+            navigator.clipboard.write([new ClipboardItem({ 'image/png': blob })]).then(function() {
+                var orig = btn.innerHTML;
+                btn.innerHTML = '<i class="bi bi-check me-2" aria-hidden="true"></i>コピーしました';
+                btn.classList.replace('btn-outline-primary', 'btn-success');
+                setTimeout(function() {
+                    btn.innerHTML = orig;
+                    btn.classList.replace('btn-success', 'btn-outline-primary');
+                }, 2000);
+            }).catch(function(err) {
+                showCopyFeedback('画像のコピーに失敗しました。「画像を保存」をご利用ください。（' + (err.message || err) + '）');
+            });
+        });
 
         function getRateClass(rate) {
             if (rate >= 80) return 'text-success';
@@ -479,22 +403,22 @@
         }
 
         function renderProgress(completed, pending, overdue, total) {
-            if (total === 0) return '<div class="progress table-progress"></div>';
+            if (total === 0) return '<div class="progress table-progress" role="progressbar" aria-valuenow="0" aria-valuemin="0" aria-valuemax="100" aria-label="進捗なし"></div>';
             var cP = (completed / total * 100).toFixed(1);
-            var pP = (pending / total * 100).toFixed(1);
-            var oP = (overdue / total * 100).toFixed(1);
-            return '<div class="progress table-progress">' +
+            var pP = (pending   / total * 100).toFixed(1);
+            var oP = (overdue   / total * 100).toFixed(1);
+            return '<div class="progress table-progress" role="progressbar" aria-valuenow="' + cP + '" aria-valuemin="0" aria-valuemax="100" aria-label="完了' + cP + '%、未完了' + pP + '%、期限切れ' + oP + '%">' +
                 '<div class="progress-bar bg-success" style="width:' + cP + '%" title="完了: ' + completed + '"></div>' +
                 '<div class="progress-bar bg-warning" style="width:' + pP + '%" title="未完了: ' + pending + '"></div>' +
-                '<div class="progress-bar bg-danger" style="width:' + oP + '%" title="期限切れ: ' + overdue + '"></div></div>';
+                '<div class="progress-bar bg-danger"  style="width:' + oP + '%" title="期限切れ: ' + overdue + '"></div></div>';
         }
 
         function renderRow(s, isArchived) {
-            var action = isArchived ?
-                '<form action="/statistics/unarchive-subject" method="POST" class="d-inline"><input type="hidden" name="_csrf" value="' + csrfToken + '"><input type="hidden" name="subject" value="' + s.subject + '"><button type="submit" class="btn btn-sm btn-outline-success" title="復元"><i class="bi bi-arrow-counterclockwise"></i></button></form>' :
-                '<form action="/statistics/archive-subject" method="POST" class="d-inline"><input type="hidden" name="_csrf" value="' + csrfToken + '"><input type="hidden" name="subject" value="' + s.subject + '"><button type="submit" class="btn btn-sm btn-outline-secondary" title="アーカイブ"><i class="bi bi-archive"></i></button></form>';
+            var action = isArchived
+                ? '<form action="/statistics/unarchive-subject" method="POST" class="d-inline"><input type="hidden" name="_csrf" value="' + csrfToken + '"><input type="hidden" name="subject" value="' + XSS.escapeHtml(s.subject) + '"><button type="submit" class="btn btn-sm btn-outline-success" aria-label="' + XSS.escapeHtml(s.subject) + 'を復元"><i class="bi bi-arrow-counterclockwise" aria-hidden="true"></i></button></form>'
+                : '<form action="/statistics/archive-subject"   method="POST" class="d-inline"><input type="hidden" name="_csrf" value="' + csrfToken + '"><input type="hidden" name="subject" value="' + XSS.escapeHtml(s.subject) + '"><button type="submit" class="btn btn-sm btn-outline-secondary" aria-label="' + XSS.escapeHtml(s.subject) + 'をアーカイブ"><i class="bi bi-archive" aria-hidden="true"></i></button></form>';
             return '<tr class="subject-row">' +
-                '<td><a href="/statistics?subject=' + encodeURIComponent(s.subject) + '" class="text-decoration-none"><i class="bi bi-folder me-1"></i>' + s.subject + '</a></td>' +
+                '<td><a href="/statistics?subject=' + encodeURIComponent(s.subject) + '" class="text-decoration-none"><i class="bi bi-folder me-1" aria-hidden="true"></i>' + XSS.escapeHtml(s.subject) + '</a></td>' +
                 '<td class="text-center">' + s.total + '</td>' +
                 '<td class="text-center text-success">' + s.completed + '</td>' +
                 '<td class="text-center text-warning">' + s.pending + '</td>' +
@@ -510,7 +434,7 @@
             if (total <= 1) return;
             var prev = document.createElement('li');
             prev.className = 'page-item' + (page === 1 ? ' disabled' : '');
-            prev.innerHTML = '<a class="page-link" href="#">&laquo;</a>';
+            prev.innerHTML = '<a class="page-link" href="#" aria-label="前のページ">&laquo;</a>';
             if (page > 1) prev.onclick = function (e) { e.preventDefault(); cb(page - 1); };
             el.appendChild(prev);
             for (var i = 1; i <= total; i++) {
@@ -522,28 +446,28 @@
             }
             var next = document.createElement('li');
             next.className = 'page-item' + (page === total ? ' disabled' : '');
-            next.innerHTML = '<a class="page-link" href="#">&raquo;</a>';
+            next.innerHTML = '<a class="page-link" href="#" aria-label="次のページ">&raquo;</a>';
             if (page < total) next.onclick = function (e) { e.preventDefault(); cb(page + 1); };
             el.appendChild(next);
         }
 
         function renderActiveSubjects() {
-            var start = (activePage - 1) * PAGE_SIZE;
-            var end = Math.min(start + PAGE_SIZE, activeSubjects.length);
+            var start      = (activePage - 1) * PAGE_SIZE;
+            var end        = Math.min(start + PAGE_SIZE, activeSubjects.length);
             var totalPages = Math.ceil(activeSubjects.length / PAGE_SIZE);
             document.getElementById('activeSubjectsBody').innerHTML = activeSubjects.slice(start, end).map(function (s) { return renderRow(s, false); }).join('');
-            document.getElementById('activeCount').textContent = activeSubjects.length;
+            document.getElementById('activeCount').textContent    = activeSubjects.length;
             document.getElementById('activePageInfo').textContent = activeSubjects.length > 0 ? (start + 1) + '-' + end + ' / ' + activeSubjects.length + ' 件' : '0 件';
             renderPagination('activePagination', activePage, totalPages, function (p) { activePage = p; renderActiveSubjects(); });
             document.getElementById('activeSubjectsCard').style.display = activeSubjects.length > 0 ? 'block' : 'none';
         }
 
         function renderArchivedSubjects() {
-            var start = (archivedPage - 1) * PAGE_SIZE;
-            var end = Math.min(start + PAGE_SIZE, archivedSubjects.length);
+            var start      = (archivedPage - 1) * PAGE_SIZE;
+            var end        = Math.min(start + PAGE_SIZE, archivedSubjects.length);
             var totalPages = Math.ceil(archivedSubjects.length / PAGE_SIZE);
             document.getElementById('archivedSubjectsBody').innerHTML = archivedSubjects.slice(start, end).map(function (s) { return renderRow(s, true); }).join('');
-            document.getElementById('archivedCount').textContent = archivedSubjects.length;
+            document.getElementById('archivedCount').textContent    = archivedSubjects.length;
             document.getElementById('archivedPageInfo').textContent = archivedSubjects.length > 0 ? (start + 1) + '-' + end + ' / ' + archivedSubjects.length + ' 件' : '0 件';
             renderPagination('archivedPagination', archivedPage, totalPages, function (p) { archivedPage = p; renderArchivedSubjects(); });
             document.getElementById('archivedSubjectsCard').style.display = archivedSubjects.length > 0 ? 'block' : 'none';
@@ -553,9 +477,9 @@
         renderArchivedSubjects();
         if (activeSubjects.length === 0 && archivedSubjects.length === 0) {
             document.getElementById('noSubjectsCard').classList.remove('d-none');
-            document.getElementById('activeSubjectsCard').style.display = 'none';
+            document.getElementById('activeSubjectsCard').style.display  = 'none';
             document.getElementById('archivedSubjectsCard').style.display = 'none';
         }
     })();
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/layouts/base.html b/web/templates/layouts/base.html
index 875d147..8ff87fc 100644
--- a/web/templates/layouts/base.html
+++ b/web/templates/layouts/base.html
@@ -8,18 +8,16 @@
     <title>{{.title}} - Super Homework Manager</title>
     <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.2/dist/css/bootstrap.min.css" rel="stylesheet">
     <link href="https://cdn.jsdelivr.net/npm/bootstrap-icons@1.11.1/font/bootstrap-icons.css" rel="stylesheet">
-    <link href="https://cdn.jsdelivr.net/npm/@fortawesome/fontawesome-free@6.5.1/css/all.min.css" rel="stylesheet">
     <link href="/static/css/style.css" rel="stylesheet">
     <style>
         .navbar-dark .navbar-nav .nav-link,
         .navbar-brand {
-            color: #fff !important;
+            color: #fff;
             transition: color 0.15s ease-in-out;
         }
-
         .navbar-dark .navbar-nav .nav-link:hover,
         .navbar-brand:hover {
-            color: rgba(255, 255, 255, 0.75) !important;
+            color: rgba(255, 255, 255, 0.75);
         }
     </style>
     {{template "head" .}}
@@ -27,53 +25,51 @@
 
 <body>
     {{if .userName}}
-    <nav class="navbar navbar-expand-lg navbar-dark bg-primary">
+    <nav class="navbar navbar-expand-lg navbar-dark bg-primary" role="navigation" aria-label="メインナビゲーション">
         <div class="container">
             <a class="navbar-brand" href="/">
-                <i class="bi bi-journal-check me-2"></i>Super Homework Manager
+                <i class="bi bi-journal-check me-2" aria-hidden="true"></i>Super Homework Manager
             </a>
-            <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarNav">
+            <button class="navbar-toggler" type="button"
+                    data-bs-toggle="collapse" data-bs-target="#navbarNav"
+                    aria-controls="navbarNav" aria-expanded="false" aria-label="ナビゲーションを開く">
                 <span class="navbar-toggler-icon"></span>
             </button>
             <div class="collapse navbar-collapse" id="navbarNav">
                 <ul class="navbar-nav me-auto">
                     <li class="nav-item">
-                        <a class="nav-link" href="/"><i class="bi bi-house-door me-1"></i>ダッシュボード</a>
+                        <a class="nav-link" href="/"><i class="bi bi-house-door me-1" aria-hidden="true"></i>ダッシュボード</a>
                     </li>
                     <li class="nav-item">
-                        <a class="nav-link" href="/assignments"><i class="bi bi-list-task me-1"></i>課題一覧</a>
+                        <a class="nav-link" href="/assignments"><i class="bi bi-list-task me-1" aria-hidden="true"></i>課題一覧</a>
                     </li>
                     <li class="nav-item">
-                        <a class="nav-link" href="/assignments/new"><i class="bi bi-plus-circle me-1"></i>課題登録</a>
-                    </li>
-                    <li class="nav-item">
-                        <a class="nav-link" href="/statistics"><i class="bi bi-bar-chart me-1"></i>統計</a>
+                        <a class="nav-link" href="/statistics"><i class="bi bi-bar-chart me-1" aria-hidden="true"></i>統計</a>
                     </li>
                     {{if .isAdmin}}
                     <li class="nav-item">
-                        <a class="nav-link" href="/admin/users"><i class="bi bi-people me-1"></i>ユーザー管理</a>
+                        <a class="nav-link" href="/admin/users"><i class="bi bi-people me-1" aria-hidden="true"></i>ユーザー管理</a>
                     </li>
                     <li class="nav-item">
-                        <a class="nav-link" href="/admin/api-keys"><i class="bi bi-key me-1"></i>APIキー管理</a>
+                        <a class="nav-link" href="/admin/api-keys"><i class="bi bi-key me-1" aria-hidden="true"></i>APIキー管理</a>
                     </li>
                     {{end}}
                 </ul>
                 <ul class="navbar-nav">
                     <li class="nav-item dropdown">
-                        <a class="nav-link dropdown-toggle" href="#" role="button" data-bs-toggle="dropdown">
-                            <i class="bi bi-person-circle me-1"></i>{{.userName}}
+                        <a class="nav-link dropdown-toggle" href="#" role="button"
+                           data-bs-toggle="dropdown" aria-expanded="false">
+                            <i class="bi bi-person-circle me-1" aria-hidden="true"></i>{{.userName}}
                         </a>
                         <ul class="dropdown-menu dropdown-menu-end">
-                            <li><a class="dropdown-item" href="/profile"><i class="bi bi-person me-2"></i>プロフィール</a>
-                            </li>
-                            <li>
-                                <hr class="dropdown-divider">
-                            </li>
+                            <li><a class="dropdown-item" href="/profile"><i class="bi bi-person me-2" aria-hidden="true"></i>プロフィール</a></li>
+                            <li><hr class="dropdown-divider"></li>
                             <li>
                                 <form action="/logout" method="POST" class="d-inline">
                                     <input type="hidden" name="_csrf" value="{{.csrfToken}}">
-                                    <button type="submit" class="dropdown-item"><i
-                                            class="bi bi-box-arrow-right me-2"></i>ログアウト</button>
+                                    <button type="submit" class="dropdown-item">
+                                        <i class="bi bi-box-arrow-right me-2" aria-hidden="true"></i>ログアウト
+                                    </button>
                                 </form>
                             </li>
                         </ul>
@@ -97,6 +93,18 @@
         </div>
     </footer>
 
+    <div class="modal fade" id="confirmModal" tabindex="-1" aria-labelledby="confirmModalLabel" aria-modal="true" role="dialog">
+        <div class="modal-dialog modal-sm modal-dialog-centered">
+            <div class="modal-content">
+                <div class="modal-body" id="confirmModalBody"></div>
+                <div class="modal-footer py-2 border-0">
+                    <button type="button" class="btn btn-secondary btn-sm" data-bs-dismiss="modal">キャンセル</button>
+                    <button type="button" class="btn btn-danger btn-sm" id="confirmModalOk">確認</button>
+                </div>
+            </div>
+        </div>
+    </div>
+
     <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.2/dist/js/bootstrap.bundle.min.js"></script>
     <script src="/static/js/app.js"></script>
     {{template "scripts" .}}
@@ -106,4 +114,4 @@
 {{end}}
 
 {{define "head"}}{{end}}
-{{define "scripts"}}{{end}}
\ No newline at end of file
+{{define "scripts"}}{{end}}
diff --git a/web/templates/pages/dashboard.html b/web/templates/pages/dashboard.html
index aa59dc3..83e1d2d 100644
--- a/web/templates/pages/dashboard.html
+++ b/web/templates/pages/dashboard.html
@@ -2,94 +2,42 @@
 
 {{define "head"}}
 <style>
-    @keyframes pulse-bg {
-
-        0%,
-        100% {
-            background-color: #fff3cd;
-        }
-
-        50% {
-            background-color: #ffe69c;
-        }
-    }
-
-    @keyframes pulse-bg-danger {
-
-        0%,
-        100% {
-            background-color: #f8d7da;
-        }
-
-        50% {
-            background-color: #f5c2c7;
-        }
-    }
-
-    @keyframes blink-banner {
-
-        0%,
-        100% {
-            opacity: 1;
-        }
-
-        50% {
-            opacity: 0.7;
-        }
-    }
-
-    .anxiety-warning {
-        animation: pulse-bg 2s infinite;
-    }
-
-    .anxiety-danger {
-        animation: pulse-bg-danger 1s infinite;
-    }
-
-    .urgent-banner {
-        z-index: 1030;
-        animation: blink-banner 1s infinite;
-    }
-
-    .urgent-banner-danger {
-        background: linear-gradient(90deg, #dc3545, #c82333);
-        color: white;
-    }
-
-    .urgent-banner-warning {
-        background: linear-gradient(90deg, #fd7e14, #e06c00);
-        color: white;
-    }
-
-    .urgent-countdown {
-        font-size: 1.5rem;
-        font-weight: bold;
-    }
-
     .dashboard-stat-card {
         transition: transform 0.2s ease, box-shadow 0.2s ease;
         cursor: pointer;
     }
-
     .dashboard-stat-card:hover {
         transform: translateY(-4px);
         box-shadow: 0 8px 25px rgba(0, 0, 0, 0.15);
     }
+    .urgent-banner-danger {
+        background: linear-gradient(90deg, #dc3545, #c82333);
+        color: white;
+    }
+    .urgent-banner-warning {
+        background: linear-gradient(90deg, #fd7e14, #e06c00);
+        color: white;
+    }
+    .urgent-countdown {
+        font-size: 1.5rem;
+        font-weight: bold;
+    }
 </style>
 {{end}}
 
 {{define "content"}}
-<div id="urgentBanner" class="urgent-banner py-3 text-center d-none">
-    <div class="container">
-        <i class="bi bi-exclamation-octagon-fill me-2"></i>
+<div id="urgentBanner" class="urgent-banner py-3 text-center d-none" role="alert" aria-live="assertive" aria-atomic="true">
+    <div class="container position-relative">
+        <i class="bi bi-exclamation-octagon-fill me-2" aria-hidden="true"></i>
         <span id="urgentMessage"></span>
         <div class="urgent-countdown mt-1">
-            <i class="bi bi-stopwatch"></i> <span id="urgentCountdown"></span>
+            <i class="bi bi-stopwatch" aria-hidden="true"></i> <span id="urgentCountdown"></span>
         </div>
+        <button type="button" id="closeBanner" class="btn-close btn-close-white position-absolute top-0 end-0" aria-label="バナーを閉じる" onclick="document.getElementById('urgentBanner').classList.add('d-none')"></button>
     </div>
 </div>
 
-<h1 class="mb-4"><i class="bi bi-house-door me-2"></i>ダッシュボード</h1>
+<h1 class="mb-4"><i class="bi bi-house-door me-2" aria-hidden="true"></i>ダッシュボード</h1>
 
 <div class="row g-4 mb-4">
     <div class="col-6 col-md-3">
@@ -101,7 +49,7 @@
                             <h6 class="text-white-50">未完了の課題</h6>
                             <h2 class="mb-0">{{.stats.TotalPending}}</h2>
                         </div>
-                        <i class="bi bi-list-task display-4 opacity-50"></i>
+                        <i class="bi bi-list-task display-4 opacity-50" aria-hidden="true"></i>
                     </div>
                 </div>
             </div>
@@ -116,7 +64,7 @@
                             <h6 class="text-dark-50">今日が期限</h6>
                             <h2 class="mb-0">{{.stats.DueToday}}</h2>
                         </div>
-                        <i class="bi bi-calendar-event display-4 opacity-50"></i>
+                        <i class="bi bi-calendar-event display-4 opacity-50" aria-hidden="true"></i>
                     </div>
                 </div>
             </div>
@@ -131,7 +79,7 @@
                             <h6 class="text-white-50">今週が期限</h6>
                             <h2 class="mb-0">{{.stats.DueThisWeek}}</h2>
                         </div>
-                        <i class="bi bi-calendar-week display-4 opacity-50"></i>
+                        <i class="bi bi-calendar-week display-4 opacity-50" aria-hidden="true"></i>
                     </div>
                 </div>
             </div>
@@ -146,7 +94,7 @@
                             <h6 class="text-white-50">期限切れ</h6>
                             <h2 class="mb-0">{{.stats.Overdue}}</h2>
                         </div>
-                        <i class="bi bi-exclamation-triangle display-4 opacity-50"></i>
+                        <i class="bi bi-exclamation-triangle display-4 opacity-50" aria-hidden="true"></i>
                     </div>
                 </div>
             </div>
@@ -158,20 +106,22 @@
     {{if .overdue}}
     <div class="col-lg-6">
         <div class="card border-danger">
-            <div class="card-header bg-danger text-white"><i class="bi bi-exclamation-triangle me-2"></i>期限切れの課題</div>
+            <div class="card-header bg-danger text-white"><i class="bi bi-exclamation-triangle me-2" aria-hidden="true"></i>期限切れの課題</div>
             <ul class="list-group list-group-flush">
                 {{range .overdue}}
-                <li class="list-group-item d-flex justify-content-between align-items-center"
-                    data-priority="{{.Priority}}" data-due="{{.DueDate.UnixMilli}}">
+                <li class="list-group-item d-flex justify-content-between align-items-center" data-priority="{{.Priority}}" data-due="{{.DueDate.UnixMilli}}">
                     <div>
                         {{if .Subject}}<span class="badge bg-secondary me-1">{{.Subject}}</span>{{end}}
-                        {{if eq .Priority "high"}}<span class="badge bg-danger me-1">重要</span>{{end}}
+                        {{if eq .Priority "high"}}<span class="badge bg-danger me-1">高<span class="visually-hidden">（重要度：高）</span></span>{{end}}
                         <strong>{{.Title}}</strong>
                         <br><small class="text-danger">{{formatDateTime .DueDate}}</small>
                     </div>
-                    <form action="/assignments/{{.ID}}/toggle" method="POST"><input type="hidden" name="_csrf"
-                            value="{{$.csrfToken}}"><button type="submit" class="btn btn-sm btn-success"
-                            title="完了にする"><i class="bi bi-check-lg"></i></button></form>
+                    <form action="/assignments/{{.ID}}/toggle" method="POST">
+                        <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
+                        <button type="submit" class="btn btn-sm btn-success" aria-label="{{.Title}}を完了にする">
+                            <i class="bi bi-check-lg" aria-hidden="true"></i>
+                        </button>
+                    </form>
                 </li>
                 {{end}}
             </ul>
@@ -181,20 +131,22 @@
     {{if .dueToday}}
     <div class="col-lg-6">
         <div class="card border-warning">
-            <div class="card-header bg-warning text-dark"><i class="bi bi-calendar-event me-2"></i>今日が期限</div>
+            <div class="card-header bg-warning text-dark"><i class="bi bi-calendar-event me-2" aria-hidden="true"></i>今日が期限</div>
             <ul class="list-group list-group-flush">
                 {{range .dueToday}}
-                <li class="list-group-item d-flex justify-content-between align-items-center"
-                    data-priority="{{.Priority}}" data-due="{{.DueDate.UnixMilli}}">
+                <li class="list-group-item d-flex justify-content-between align-items-center" data-priority="{{.Priority}}" data-due="{{.DueDate.UnixMilli}}">
                     <div>
                         {{if .Subject}}<span class="badge bg-secondary me-1">{{.Subject}}</span>{{end}}
-                        {{if eq .Priority "high"}}<span class="badge bg-danger me-1">重要</span>{{end}}
+                        {{if eq .Priority "high"}}<span class="badge bg-danger me-1">高<span class="visually-hidden">（重要度：高）</span></span>{{end}}
                         <strong>{{.Title}}</strong>
                         <br><small class="text-muted">{{formatDateTime .DueDate}}</small>
                     </div>
-                    <form action="/assignments/{{.ID}}/toggle" method="POST"><input type="hidden" name="_csrf"
-                            value="{{$.csrfToken}}"><button type="submit" class="btn btn-sm btn-success"
-                            title="完了にする"><i class="bi bi-check-lg"></i></button></form>
+                    <form action="/assignments/{{.ID}}/toggle" method="POST">
+                        <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
+                        <button type="submit" class="btn btn-sm btn-success" aria-label="{{.Title}}を完了にする">
+                            <i class="bi bi-check-lg" aria-hidden="true"></i>
+                        </button>
+                    </form>
                 </li>
                 {{end}}
             </ul>
@@ -204,20 +156,22 @@
     {{if .upcoming}}
     <div class="col-lg-6">
         <div class="card border-info">
-            <div class="card-header bg-info text-white"><i class="bi bi-calendar-week me-2"></i>今週の課題</div>
+            <div class="card-header bg-info text-white"><i class="bi bi-calendar-week me-2" aria-hidden="true"></i>今週の課題</div>
             <ul class="list-group list-group-flush">
                 {{range .upcoming}}
-                <li class="list-group-item d-flex justify-content-between align-items-center"
-                    data-priority="{{.Priority}}" data-due="{{.DueDate.UnixMilli}}">
+                <li class="list-group-item d-flex justify-content-between align-items-center" data-priority="{{.Priority}}" data-due="{{.DueDate.UnixMilli}}">
                     <div>
                         {{if .Subject}}<span class="badge bg-secondary me-1">{{.Subject}}</span>{{end}}
-                        {{if eq .Priority "high"}}<span class="badge bg-danger me-1">重要</span>{{end}}
+                        {{if eq .Priority "high"}}<span class="badge bg-danger me-1">高<span class="visually-hidden">（重要度：高）</span></span>{{end}}
                         <strong>{{.Title}}</strong>
                         <br><small class="text-muted">{{formatDateTime .DueDate}}</small>
                     </div>
-                    <form action="/assignments/{{.ID}}/toggle" method="POST"><input type="hidden" name="_csrf"
-                            value="{{$.csrfToken}}"><button type="submit" class="btn btn-sm btn-success"
-                            title="完了にする"><i class="bi bi-check-lg"></i></button></form>
+                    <form action="/assignments/{{.ID}}/toggle" method="POST">
+                        <input type="hidden" name="_csrf" value="{{$.csrfToken}}">
+                        <button type="submit" class="btn btn-sm btn-success" aria-label="{{.Title}}を完了にする">
+                            <i class="bi bi-check-lg" aria-hidden="true"></i>
+                        </button>
+                    </form>
                 </li>
                 {{end}}
             </ul>
@@ -228,10 +182,10 @@
 
 {{if and (not .overdue) (not .dueToday) (not .upcoming)}}
 <div class="text-center py-5">
-    <i class="bi bi-emoji-smile display-1 text-success"></i>
+    <i class="bi bi-emoji-smile display-1 text-success" aria-hidden="true"></i>
     <h3 class="mt-3">今週の課題はありません！</h3>
     <p class="text-muted">新しい課題を登録しましょう</p>
-    <a href="/assignments/new" class="btn btn-primary"><i class="bi bi-plus-circle me-1"></i>課題を登録</a>
+    <a href="/assignments/new" class="btn btn-primary"><i class="bi bi-plus-circle me-1" aria-hidden="true"></i>課題を登録</a>
 </div>
 {{end}}
 {{end}}
@@ -239,20 +193,20 @@
 {{define "scripts"}}
 <script>
     (function () {
-        var banner = document.getElementById('urgentBanner');
-        var message = document.getElementById('urgentMessage');
+        var banner    = document.getElementById('urgentBanner');
+        var message   = document.getElementById('urgentMessage');
         var countdown = document.getElementById('urgentCountdown');
-        var body = document.body;
+
+        var reduced = window.matchMedia && window.matchMedia('(prefers-reduced-motion: reduce)').matches;
 
         var items = document.querySelectorAll('[data-priority="high"][data-due]');
         var mostUrgent = null;
         var mostUrgentDue = Infinity;
 
         items.forEach(function (item) {
-            var due = parseInt(item.dataset.due);
-            var now = Date.now();
+            var due  = parseInt(item.dataset.due);
+            var now  = Date.now();
             var diff = due - now;
-
             if (diff > 0 && diff < mostUrgentDue) {
                 mostUrgentDue = diff;
                 var titleEl = item.querySelector('strong');
@@ -260,59 +214,47 @@
             }
         });
 
-        var hasOverdueHigh = false;
-        var overdueItems = document.querySelectorAll('[data-priority="high"]');
-        overdueItems.forEach(function (item) {
+        var hasOverdueHigh = Array.from(document.querySelectorAll('[data-priority="high"]')).some(function(item) {
             var due = parseInt(item.dataset.due);
-            if (due && due < Date.now()) {
-                hasOverdueHigh = true;
-            }
+            return due && due < Date.now();
         });
 
         if (hasOverdueHigh) {
             banner.classList.remove('d-none');
             banner.classList.add('urgent-banner-danger');
-            message.innerHTML = '🚨 <strong>期限切れの重要課題があります！</strong>';
+            if (!reduced) banner.classList.add('anxiety-danger');
+            message.textContent = '期限切れの重要課題があります！';
             countdown.textContent = '今すぐ対応してください！';
-            body.classList.add('anxiety-danger');
         } else if (mostUrgent && mostUrgentDue < 24 * 60 * 60 * 1000) {
             banner.classList.remove('d-none');
             banner.classList.add('urgent-banner-danger');
-            message.innerHTML = '🚨 <strong>「' + mostUrgent.title + '」の期限が迫っています！</strong>';
-            body.classList.add('anxiety-danger');
+            if (!reduced) banner.classList.add('anxiety-danger');
+            message.textContent = '「' + mostUrgent.title + '」の期限が迫っています！';
             updateCountdown();
-            setInterval(updateCountdown, 1000);
+            if (!reduced) setInterval(updateCountdown, 1000);
         } else if (mostUrgent && mostUrgentDue < 3 * 24 * 60 * 60 * 1000) {
             banner.classList.remove('d-none');
             banner.classList.add('urgent-banner-warning');
-            message.innerHTML = '⚠️ <strong>「' + mostUrgent.title + '」の期限が近づいています</strong>';
-            body.classList.add('anxiety-warning');
+            if (!reduced) banner.classList.add('anxiety-warning');
+            message.textContent = '「' + mostUrgent.title + '」の期限が近づいています';
             updateCountdown();
-            setInterval(updateCountdown, 1000);
+            if (!reduced) setInterval(updateCountdown, 60000);
         }
 
         function updateCountdown() {
             if (!mostUrgent) return;
-            var now = Date.now();
-            var diff = mostUrgent.due - now;
-
-            if (diff <= 0) {
-                countdown.textContent = '期限切れ！';
-                return;
-            }
-
-            var days = Math.floor(diff / 86400000);
+            var diff = mostUrgent.due - Date.now();
+            if (diff <= 0) { countdown.textContent = '期限切れ！'; return; }
+            var days  = Math.floor(diff / 86400000);
             var hours = Math.floor((diff % 86400000) / 3600000);
-            var mins = Math.floor((diff % 3600000) / 60000);
-            var secs = Math.floor((diff % 60000) / 1000);
-
-            var text = 'あと ';
+            var mins  = Math.floor((diff % 3600000) / 60000);
+            var secs  = Math.floor((diff % 60000) / 1000);
+            var text  = 'あと ';
             if (days > 0) text += days + '日 ' + hours + '時間 ' + mins + '分 ' + secs + '秒';
             else if (hours > 0) text += hours + '時間 ' + mins + '分 ' + secs + '秒';
             else text += mins + '分 ' + secs + '秒';
-
             countdown.textContent = text;
         }
     })();
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/pages/error.html b/web/templates/pages/error.html
index ec07e1a..4a17ae9 100644
--- a/web/templates/pages/error.html
+++ b/web/templates/pages/error.html
@@ -1,10 +1,18 @@
 {{template "base" .}}
 
 {{define "content"}}
-<div class="text-center py-5">
-    <i class="bi bi-exclamation-triangle display-1 text-danger"></i>
+<div class="text-center py-5" role="main">
+    <i class="bi bi-exclamation-triangle display-1 text-danger" aria-hidden="true"></i>
     <h1 class="mt-4">{{.title}}</h1>
     <p class="lead text-muted">{{.message}}</p>
-    <a href="/" class="btn btn-primary mt-3"><i class="bi bi-house-door me-1"></i>ダッシュボードに戻る</a>
+    <p class="text-muted small">問題が続く場合はページを再読み込みするか、最初からやり直してください。</p>
+    <div class="d-flex justify-content-center gap-2 mt-3">
+        <button type="button" class="btn btn-outline-secondary" onclick="location.reload()">
+            <i class="bi bi-arrow-clockwise me-1" aria-hidden="true"></i>再読み込み
+        </button>
+        <a href="/" class="btn btn-primary">
+            <i class="bi bi-house-door me-1" aria-hidden="true"></i>ダッシュボードに戻る
+        </a>
+    </div>
 </div>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/pages/profile.html b/web/templates/pages/profile.html
index 4451dad..7a0f1e7 100644
--- a/web/templates/pages/profile.html
+++ b/web/templates/pages/profile.html
@@ -3,7 +3,7 @@
 {{define "content"}}
 <div class="row justify-content-center">
     <div class="col-lg-10">
-        <h1 class="mb-4"><i class="bi bi-person me-2"></i>プロフィール</h1>
+        <h1 class="mb-4"><i class="bi bi-person me-2" aria-hidden="true"></i>プロフィール</h1>
         <div class="row g-4">
             <div class="col-md-6">
                 <div class="card">
@@ -11,25 +11,23 @@
                         <h5 class="mb-0">アカウント情報</h5>
                     </div>
                     <div class="card-body">
-                        {{if .error}}<div class="alert alert-danger">{{.error}}</div>{{end}}
-                        {{if .success}}<div class="alert alert-success">{{.success}}</div>{{end}}
+                        {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
+                        {{if .success}}<div class="alert alert-success" role="status">{{.success}}</div>{{end}}
                         <form method="POST" action="/profile">
                             {{.csrfField}}
                             <div class="mb-3">
-                                <label for="email" class="form-label">メールアドレス</label>
-                                <input type="email" class="form-control" id="email" value="{{.user.Email}}" disabled>
+                                <p class="form-label mb-1 text-muted small">メールアドレス</p>
+                                <p class="mb-0 fw-bold">{{.user.Email}}</p>
                             </div>
                             <div class="mb-3">
                                 <label for="name" class="form-label">名前</label>
-                                <input type="text" class="form-control" id="name" name="name" value="{{.user.Name}}"
-                                    required>
+                                <input type="text" class="form-control" id="name" name="name" value="{{.user.Name}}" required>
                             </div>
                             <div class="mb-3">
-                                <label class="form-label">ロール</label>
-                                <input type="text" class="form-control"
-                                    value="{{if eq .user.Role `admin`}}管理者{{else}}ユーザー{{end}}" disabled>
+                                <p class="form-label mb-1 text-muted small">ロール</p>
+                                <p class="mb-0 fw-bold">{{if eq .user.Role "admin"}}管理者{{else}}ユーザー{{end}}</p>
                             </div>
-                            <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1"></i>更新</button>
+                            <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1" aria-hidden="true"></i>更新</button>
                         </form>
                     </div>
                 </div>
@@ -40,111 +38,101 @@
                         <h5 class="mb-0">パスワード変更</h5>
                     </div>
                     <div class="card-body">
-                        {{if .passwordError}}<div class="alert alert-danger">{{.passwordError}}</div>{{end}}
-                        {{if .passwordSuccess}}<div class="alert alert-success">{{.passwordSuccess}}</div>{{end}}
+                        {{if .passwordError}}<div class="alert alert-danger" role="alert">{{.passwordError}}</div>{{end}}
+                        {{if .passwordSuccess}}<div class="alert alert-success" role="status">{{.passwordSuccess}}</div>{{end}}
                         <form method="POST" action="/profile/password">
                             {{.csrfField}}
                             <div class="mb-3">
                                 <label for="old_password" class="form-label">現在のパスワード</label>
-                                <input type="password" class="form-control" id="old_password" name="old_password"
-                                    required>
+                                <input type="password" class="form-control" id="old_password" name="old_password" required autocomplete="current-password">
                             </div>
                             <div class="mb-3">
                                 <label for="new_password" class="form-label">新しいパスワード</label>
-                                <input type="password" class="form-control" id="new_password" name="new_password"
-                                    required minlength="6">
-                                <div class="form-text">6文字以上</div>
+                                <input type="password" class="form-control" id="new_password" name="new_password" required minlength="8" autocomplete="new-password">
+                                <div class="form-text">8文字以上</div>
                             </div>
                             <div class="mb-3">
                                 <label for="confirm_password" class="form-label">新しいパスワード（確認）</label>
-                                <input type="password" class="form-control" id="confirm_password"
-                                    name="confirm_password" required>
+                                <input type="password" class="form-control" id="confirm_password" name="confirm_password" required minlength="8" autocomplete="new-password">
                             </div>
-                            <button type="submit" class="btn btn-warning"><i class="bi bi-key me-1"></i>パスワード変更</button>
+                            <button type="submit" class="btn btn-primary"><i class="bi bi-key me-1" aria-hidden="true"></i>パスワード変更</button>
                         </form>
                     </div>
                 </div>
             </div>
         </div>
 
-        <!-- 2段階認証設定 -->
         <div class="card mt-4">
             <div class="card-header">
-                <h5 class="mb-0"><i class="bi bi-shield-lock me-2"></i>2段階認証（2FA）</h5>
+                <h5 class="mb-0"><i class="bi bi-shield-lock me-2" aria-hidden="true"></i>2段階認証（2FA）</h5>
             </div>
             <div class="card-body">
-                {{if .totpError}}<div class="alert alert-danger">{{.totpError}}</div>{{end}}
-                {{if .totpSuccess}}<div class="alert alert-success">{{.totpSuccess}}</div>{{end}}
+                {{if .totpError}}<div class="alert alert-danger" role="alert">{{.totpError}}</div>{{end}}
+                {{if .totpSuccess}}<div class="alert alert-success" role="status">{{.totpSuccess}}</div>{{end}}
                 {{if .user.TOTPEnabled}}
                 <div class="d-flex align-items-center mb-3">
-                    <span class="badge bg-success me-2"><i class="bi bi-check-lg me-1"></i>有効</span>
+                    <span class="badge bg-success me-2"><i class="bi bi-check-lg me-1" aria-hidden="true"></i>有効</span>
                     <span class="text-muted">2段階認証が有効になっています</span>
                 </div>
                 <form method="POST" action="/profile/totp/disable">
                     {{.csrfField}}
                     <div class="mb-3">
                         <label for="totp_disable_password" class="form-label">現在のパスワードを入力して無効化</label>
-                        <input type="password" class="form-control" id="totp_disable_password" name="password"
-                            placeholder="パスワード" required style="max-width:320px">
+                        <input type="password" class="form-control" id="totp_disable_password" name="password" placeholder="パスワード" required style="max-width:320px" autocomplete="current-password">
                     </div>
                     <button type="submit" class="btn btn-danger">
-                        <i class="bi bi-shield-x me-1"></i>2段階認証を無効化
+                        <i class="bi bi-shield-x me-1" aria-hidden="true"></i>2段階認証を無効化
                     </button>
                 </form>
                 {{else}}
                 <div class="d-flex align-items-center mb-3">
-                    <span class="badge bg-secondary me-2"><i class="bi bi-x-lg me-1"></i>無効</span>
+                    <span class="badge bg-secondary me-2"><i class="bi bi-x-lg me-1" aria-hidden="true"></i>無効</span>
                     <span class="text-muted">2段階認証が設定されていません</span>
                 </div>
                 <p class="text-muted small">2段階認証を有効にするとセキュリティが向上します。Google Authenticator などのアプリが必要です。</p>
                 <a href="/profile/totp/setup" class="btn btn-primary">
-                    <i class="bi bi-shield-plus me-1"></i>2段階認証を設定する
+                    <i class="bi bi-shield-plus me-1" aria-hidden="true"></i>2段階認証を設定する
                 </a>
                 {{end}}
             </div>
         </div>
 
-        <!-- 通知設定 -->
         <div class="card mt-4">
             <div class="card-header">
-                <h5 class="mb-0"><i class="bi bi-bell me-2"></i>通知設定</h5>
+                <h5 class="mb-0"><i class="bi bi-bell me-2" aria-hidden="true"></i>通知設定</h5>
             </div>
             <div class="card-body">
-                {{if .notifyError}}<div class="alert alert-danger">{{.notifyError}}</div>{{end}}
-                {{if .notifySuccess}}<div class="alert alert-success">{{.notifySuccess}}</div>{{end}}
+                {{if .notifyError}}<div class="alert alert-danger" role="alert">{{.notifyError}}</div>{{end}}
+                {{if .notifySuccess}}<div class="alert alert-success" role="status">{{.notifySuccess}}</div>{{end}}
                 <form method="POST" action="/profile/notifications">
                     {{.csrfField}}
                     <div class="row">
                         <div class="col-md-6">
-                            <h6 class="mb-3"><i class="bi bi-telegram me-1"></i>Telegram</h6>
+                            <h6 class="mb-3"><i class="bi bi-telegram me-1" aria-hidden="true"></i>Telegram</h6>
                             <div class="form-check form-switch mb-2">
-                                <input class="form-check-input" type="checkbox" id="telegram_enabled"
-                                    name="telegram_enabled" {{if .notifySettings.TelegramEnabled}}checked{{end}}>
+                                <input class="form-check-input" type="checkbox" id="telegram_enabled" name="telegram_enabled" {{if .notifySettings.TelegramEnabled}}checked{{end}}>
                                 <label class="form-check-label" for="telegram_enabled">Telegram通知を有効化</label>
                             </div>
                             <div class="mb-3">
                                 <label for="telegram_chat_id" class="form-label">Chat ID</label>
-                                <input type="text" class="form-control" id="telegram_chat_id" name="telegram_chat_id"
-                                    value="{{.notifySettings.TelegramChatID}}" placeholder="例: 123456789">
+                                <input type="text" class="form-control" id="telegram_chat_id" name="telegram_chat_id" value="{{.notifySettings.TelegramChatID}}" placeholder="例: 123456789">
                                 <div class="form-text">
-                                    Botに<code>/start</code>を送信後、<a href="https://t.me/userinfobot"
-                                        target="_blank">@userinfobot</a>でIDを確認
+                                    Botに<code>/start</code>を送信後、<a href="https://t.me/userinfobot" target="_blank" rel="noopener noreferrer">@userinfobot</a>でIDを確認
                                 </div>
                             </div>
                         </div>
                     </div>
                     <hr class="my-3">
                     <div class="form-check form-switch mb-3">
-                        <input class="form-check-input" type="checkbox" id="notify_on_create" name="notify_on_create"
-                            {{if .notifySettings.NotifyOnCreate}}checked{{end}}>
+                        <input class="form-check-input" type="checkbox" id="notify_on_create" name="notify_on_create" {{if .notifySettings.NotifyOnCreate}}checked{{end}}>
                         <label class="form-check-label" for="notify_on_create">
-                            <i class="bi bi-plus-circle me-1"></i>課題追加時に通知する
+                            <i class="bi bi-plus-circle me-1" aria-hidden="true"></i>課題追加時に通知する
                         </label>
                     </div>
-                    <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1"></i>通知設定を保存</button>
+                    <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1" aria-hidden="true"></i>通知設定を保存</button>
                 </form>
             </div>
         </div>
     </div>
 </div>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/pages/totp_setup.html b/web/templates/pages/totp_setup.html
index 6c7241a..fbecef5 100644
--- a/web/templates/pages/totp_setup.html
+++ b/web/templates/pages/totp_setup.html
@@ -5,15 +5,15 @@
     <div class="col-md-7 col-lg-6">
         <div class="card shadow">
             <div class="card-header">
-                <h5 class="mb-0"><i class="bi bi-shield-lock me-2"></i>2段階認証の設定</h5>
+                <h5 class="mb-0"><i class="bi bi-shield-lock me-2" aria-hidden="true"></i>2段階認証の設定</h5>
             </div>
             <div class="card-body p-4">
                 {{if .error}}
-                <div class="alert alert-danger">{{.error}}</div>
+                <div class="alert alert-danger" role="alert">{{.error}}</div>
                 {{end}}
 
-                <div class="alert alert-info">
-                    <i class="bi bi-info-circle me-1"></i>
+                <div class="alert alert-info" role="note">
+                    <i class="bi bi-info-circle me-1" aria-hidden="true"></i>
                     Google Authenticator、Authy などの認証アプリを使用してください。
                 </div>
 
@@ -25,17 +25,16 @@
                 </ol>
 
                 <div class="text-center mb-4">
-                    <img src="data:image/png;base64,{{.qrCode}}" alt="QRコード" class="border rounded"
-                        style="max-width:200px">
+                    <img src="data:image/png;base64,{{.qrCode}}" alt="2段階認証設定用QRコード" class="border rounded" style="max-width:200px">
+                    <p class="text-muted small mt-2">QRコードを再スキャンしたい場合はページを再読み込みしてください。</p>
                 </div>
 
                 <div class="mb-4">
-                    <label class="form-label fw-bold">シークレットキー（手動入力の場合）</label>
+                    <label class="form-label fw-bold" for="secretKey">シークレットキー（手動入力の場合）</label>
                     <div class="input-group">
-                        <input type="text" class="form-control font-monospace" id="secretKey" value="{{.secret}}"
-                            readonly>
-                        <button class="btn btn-outline-secondary" type="button" onclick="copySecret()" title="コピー">
-                            <i class="bi bi-clipboard"></i>
+                        <input type="text" class="form-control font-monospace" id="secretKey" value="{{.secret}}" readonly aria-label="シークレットキー">
+                        <button class="btn btn-outline-secondary" type="button" id="copySecretBtn" aria-label="シークレットキーをコピー">
+                            <i class="bi bi-clipboard" aria-hidden="true"></i>
                         </button>
                     </div>
                     <div class="form-text">認証アプリで「手動入力」を選択し、このキーを入力してください。</div>
@@ -45,19 +44,16 @@
                     {{.csrfField}}
                     <div class="mb-3">
                         <label for="totp_password" class="form-label fw-bold">現在のパスワード</label>
-                        <input type="password" class="form-control" id="totp_password" name="password"
-                            placeholder="パスワードを入力" required>
+                        <input type="password" class="form-control" id="totp_password" name="password" placeholder="パスワードを入力" required autocomplete="current-password">
                     </div>
                     <div class="mb-3">
                         <label for="totp_code" class="form-label fw-bold">認証コードで確認</label>
-                        <input type="text" class="form-control form-control-lg text-center" id="totp_code"
-                            name="totp_code" placeholder="000000" maxlength="6" pattern="[0-9]{6}" inputmode="numeric"
-                            autocomplete="off" autofocus required>
+                        <input type="text" class="form-control form-control-lg text-center" id="totp_code" name="totp_code" placeholder="000000" maxlength="6" pattern="[0-9]{6}" inputmode="numeric" autocomplete="off" autofocus required>
                         <div class="form-text">認証アプリに表示された6桁のコードを入力してください。</div>
                     </div>
                     <div class="d-flex gap-2">
                         <button type="submit" class="btn btn-primary">
-                            <i class="bi bi-shield-check me-1"></i>有効化
+                            <i class="bi bi-shield-check me-1" aria-hidden="true"></i>有効化
                         </button>
                         <a href="/profile" class="btn btn-outline-secondary">キャンセル</a>
                     </div>
@@ -70,14 +66,23 @@
 
 {{define "scripts"}}
 <script>
-    function copySecret() {
-        const el = document.getElementById('secretKey');
-        el.select();
-        navigator.clipboard.writeText(el.value).then(() => {
-            const btn = el.nextElementSibling;
-            btn.innerHTML = '<i class="bi bi-check-lg"></i>';
-            setTimeout(() => { btn.innerHTML = '<i class="bi bi-clipboard"></i>'; }, 2000);
+    document.getElementById('copySecretBtn').addEventListener('click', function() {
+        var btn = this;
+        var val = document.getElementById('secretKey').value;
+        if (!navigator.clipboard) {
+            showCopyFeedback('クリップボードがサポートされていません。手動でコピーしてください。');
+            return;
+        }
+        navigator.clipboard.writeText(val).then(function() {
+            btn.innerHTML = '<i class="bi bi-check-lg" aria-hidden="true"></i>';
+            btn.setAttribute('aria-label', 'コピーしました');
+            setTimeout(function() {
+                btn.innerHTML = '<i class="bi bi-clipboard" aria-hidden="true"></i>';
+                btn.setAttribute('aria-label', 'シークレットキーをコピー');
+            }, 2000);
+        }).catch(function(err) {
+            showCopyFeedback('コピーに失敗しました: ' + (err.message || err));
         });
-    }
+    });
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/recurring/edit.html b/web/templates/recurring/edit.html
index b24445f..185c7d0 100644
--- a/web/templates/recurring/edit.html
+++ b/web/templates/recurring/edit.html
@@ -5,14 +5,14 @@
     <div class="col-lg-6">
         <div class="card shadow">
             <div class="card-header">
-                <h5 class="mb-0"><i class="bi bi-arrow-repeat me-2"></i>繰り返し課題の編集</h5>
+                <h5 class="mb-0"><i class="bi bi-arrow-repeat me-2" aria-hidden="true"></i>繰り返し課題の編集</h5>
             </div>
             <div class="card-body">
-                {{if .error}}<div class="alert alert-danger">{{.error}}</div>{{end}}
+                {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
                 <form method="POST" action="/recurring/{{.recurring.ID}}">
                     {{.csrfField}}
                     <div class="mb-3">
-                        <label for="title" class="form-label">タイトル <span class="text-danger">*</span></label>
+                        <label for="title" class="form-label">タイトル <span class="text-danger" aria-hidden="true">*</span><span class="visually-hidden">（必須）</span></label>
                         <input type="text" class="form-control" id="title" name="title" value="{{.recurring.Title}}" required>
                     </div>
                     <div class="mb-3">
@@ -22,9 +22,9 @@
                     <div class="mb-3">
                         <label for="priority" class="form-label">重要度</label>
                         <select class="form-select" id="priority" name="priority">
-                            <option value="low" {{if eq .recurring.Priority "low"}}selected{{end}}>小</option>
+                            <option value="low"    {{if eq .recurring.Priority "low"   }}selected{{end}}>低</option>
                             <option value="medium" {{if eq .recurring.Priority "medium"}}selected{{end}}>中</option>
-                            <option value="high" {{if eq .recurring.Priority "high"}}selected{{end}}>大</option>
+                            <option value="high"   {{if eq .recurring.Priority "high"  }}selected{{end}}>高</option>
                         </select>
                     </div>
                     <div class="mb-3">
@@ -35,30 +35,30 @@
                         <label for="due_time" class="form-label">時刻</label>
                         <input type="time" class="form-control" id="due_time" name="due_time" value="{{.recurring.DueTime}}">
                     </div>
-                    
+
                     <div class="card bg-light mb-3">
                         <div class="card-body py-3">
-                            <h6 class="mb-3"><i class="bi bi-arrow-repeat me-1"></i>繰り返し設定</h6>
+                            <h6 class="mb-3"><i class="bi bi-arrow-repeat me-1" aria-hidden="true"></i>繰り返し設定</h6>
                             <div class="row mb-3">
                                 <div class="col-6">
                                     <label for="recurrence_type" class="form-label small">繰り返しタイプ</label>
                                     <select class="form-select form-select-sm" id="recurrence_type" name="recurrence_type" onchange="updateRecurrenceOptions()">
-                                        <option value="daily" {{if eq .recurring.RecurrenceType "daily"}}selected{{end}}>毎日</option>
-                                        <option value="weekly" {{if eq .recurring.RecurrenceType "weekly"}}selected{{end}}>毎週</option>
+                                        <option value="daily"   {{if eq .recurring.RecurrenceType "daily"  }}selected{{end}}>毎日</option>
+                                        <option value="weekly"  {{if eq .recurring.RecurrenceType "weekly" }}selected{{end}}>毎週</option>
                                         <option value="monthly" {{if eq .recurring.RecurrenceType "monthly"}}selected{{end}}>毎月</option>
                                     </select>
                                 </div>
                                 <div class="col-6">
                                     <label for="recurrence_interval" class="form-label small">間隔</label>
                                     <div class="input-group input-group-sm">
-                                        <input type="number" class="form-control" id="recurrence_interval" name="recurrence_interval" value="{{.recurring.RecurrenceInterval}}" min="1" max="12">
+                                        <input type="number" class="form-control" id="recurrence_interval" name="recurrence_interval" value="{{.recurring.RecurrenceInterval}}" min="1" max="12" onchange="updateLeadDaysMax()">
                                         <span class="input-group-text" id="interval_label">{{if eq .recurring.RecurrenceType "daily"}}日{{else if eq .recurring.RecurrenceType "weekly"}}週{{else}}月{{end}}</span>
                                     </div>
                                 </div>
                             </div>
                             <div id="weekday_group" class="mb-3">
                                 <label class="form-label small">曜日</label>
-                                <div class="btn-group btn-group-sm w-100" role="group">
+                                <div class="btn-group btn-group-sm w-100" role="group" aria-label="曜日選択">
                                     <input type="radio" class="btn-check" name="recurrence_weekday" id="wd0" value="0" {{if .recurring.RecurrenceWeekday}}{{if eq (derefInt .recurring.RecurrenceWeekday) 0}}checked{{end}}{{end}}>
                                     <label class="btn btn-outline-primary" for="wd0">日</label>
                                     <input type="radio" class="btn-check" name="recurrence_weekday" id="wd1" value="1" {{if .recurring.RecurrenceWeekday}}{{if eq (derefInt .recurring.RecurrenceWeekday) 1}}checked{{end}}{{end}}>
@@ -83,7 +83,18 @@
                                     {{end}}
                                 </select>
                             </div>
-                            
+
+                            <div class="mb-3">
+                                <label class="form-label small">リストに追加するタイミング</label>
+                                <div class="d-flex align-items-center gap-2">
+                                    <div class="input-group input-group-sm" style="width: 120px;">
+                                        <input type="number" class="form-control" id="generation_lead_days" name="generation_lead_days" value="{{.recurring.GenerationLeadDays}}" min="0" max="365">
+                                        <span class="input-group-text">日前</span>
+                                    </div>
+                                    <input type="time" class="form-control form-control-sm" id="generation_lead_time" name="generation_lead_time" value="{{.recurring.GenerationLeadTime}}" style="width: 110px;">
+                                </div>
+                                <div class="form-text small text-muted" id="lead_days_hint"></div>
+                            </div>
                             <hr class="my-2">
                             <div class="d-flex justify-content-between align-items-center">
                                 <span class="small text-muted">状態:</span>
@@ -95,25 +106,25 @@
                             </div>
                         </div>
                     </div>
-                    
+
                     <div class="d-flex gap-2 flex-wrap">
-                        <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1"></i>更新</button>
+                        <button type="submit" class="btn btn-primary"><i class="bi bi-check-lg me-1" aria-hidden="true"></i>更新</button>
                         <a href="/assignments" class="btn btn-outline-secondary">キャンセル</a>
                         {{if .recurring.IsActive}}
-                        <button type="button" class="btn btn-outline-danger" onclick="if(confirm('繰り返しを停止しますか？今後新しい課題は自動作成されなくなります。')) document.getElementById('stopForm').submit();">
-                            <i class="bi bi-stop-fill me-1"></i>停止
+                        <button type="button" class="btn btn-outline-danger" id="stopBtn">
+                            <i class="bi bi-stop-fill me-1" aria-hidden="true"></i>停止
                         </button>
                         {{else}}
                         <button type="button" class="btn btn-outline-success" onclick="document.getElementById('resumeForm').submit();">
-                            <i class="bi bi-play-fill me-1"></i>再開
+                            <i class="bi bi-play-fill me-1" aria-hidden="true"></i>再開
                         </button>
                         {{end}}
-                        <button type="button" class="btn btn-outline-danger ms-auto" onclick="if(confirm('この繰り返し設定を削除しますか？この操作は取り消せません。')) document.getElementById('deleteForm').submit();">
-                            <i class="bi bi-trash me-1"></i>削除
+                        <button type="button" class="btn btn-outline-danger ms-auto" id="deleteBtn">
+                            <i class="bi bi-trash me-1" aria-hidden="true"></i>削除
                         </button>
                     </div>
                 </form>
-                
+
                 {{if .recurring.IsActive}}
                 <form id="stopForm" action="/recurring/{{.recurring.ID}}/stop" method="POST" class="d-none">
                     {{.csrfField}}
@@ -132,17 +143,58 @@
 </div>
 
 <script>
+    function getLeadDaysMax() {
+        var type     = document.getElementById('recurrence_type').value;
+        var interval = parseInt(document.getElementById('recurrence_interval').value) || 1;
+        if (type === 'daily')   return interval;
+        if (type === 'weekly')  return interval * 7;
+        if (type === 'monthly') return interval * 28;
+        return 0;
+    }
+    function updateLeadDaysMax() {
+        var max   = getLeadDaysMax();
+        var input = document.getElementById('generation_lead_days');
+        input.max = max;
+        if (parseInt(input.value) > max) input.value = max;
+        var type     = document.getElementById('recurrence_type').value;
+        var labels   = { daily: '日', weekly: '週', monthly: 'ヶ月' };
+        var interval = document.getElementById('recurrence_interval').value;
+        document.getElementById('lead_days_hint').textContent =
+            max === 0 ? '間隔が1日のため、事前追加は設定できません' :
+            '最大' + max + '日前まで指定可能（繰り返し間隔' + interval + labels[type] + '以内）';
+    }
     function updateRecurrenceOptions() {
         var type = document.getElementById('recurrence_type').value;
-        document.getElementById('weekday_group').style.display = type === 'weekly' ? 'block' : 'none';
-        document.getElementById('day_group').style.display = type === 'monthly' ? 'block' : 'none';
+        document.getElementById('weekday_group').style.display = type === 'weekly'  ? 'block' : 'none';
+        document.getElementById('day_group').style.display     = type === 'monthly' ? 'block' : 'none';
         var label = document.getElementById('interval_label');
-        if (type === 'daily') label.textContent = '日';
-        else if (type === 'weekly') label.textContent = '週';
-        else if (type === 'monthly') label.textContent = '月';
+        if (label) {
+            if (type === 'daily')   label.textContent = '日';
+            else if (type === 'weekly')  label.textContent = '週';
+            else if (type === 'monthly') label.textContent = '月';
+        }
+        updateLeadDaysMax();
     }
-    document.addEventListener('DOMContentLoaded', function() {
+    document.addEventListener('DOMContentLoaded', function () {
         updateRecurrenceOptions();
+
+        var stopBtn = document.getElementById('stopBtn');
+        if (stopBtn) {
+            stopBtn.addEventListener('click', function() {
+                showConfirmModal('繰り返しを停止しますか？今後新しい課題は自動作成されなくなります。', function() {
+                    document.getElementById('stopForm').submit();
+                });
+            });
+        }
+
+        var deleteBtn = document.getElementById('deleteBtn');
+        if (deleteBtn) {
+            deleteBtn.addEventListener('click', function() {
+                showConfirmModal('この繰り返し設定を削除しますか？この操作は取り消せません。', function() {
+                    document.getElementById('deleteForm').submit();
+                });
+            });
+        }
     });
 </script>
-{{end}}
\ No newline at end of file
+{{end}}
diff --git a/web/templates/recurring/index.html b/web/templates/recurring/index.html
index 1683763..4529464 100644
--- a/web/templates/recurring/index.html
+++ b/web/templates/recurring/index.html
@@ -2,24 +2,22 @@
 
 {{define "content"}}
 <div class="d-flex justify-content-between align-items-center mb-3">
-    <div class="d-flex align-items-center">
-        <h4 class="mb-0 fw-bold"><i class="bi bi-arrow-repeat me-2"></i>繰り返し設定一覧</h4>
-    </div>
+    <h4 class="mb-0 fw-bold"><i class="bi bi-arrow-repeat me-2" aria-hidden="true"></i>繰り返し設定一覧</h4>
     <a href="/assignments" class="btn btn-sm btn-outline-secondary">
-        <i class="bi bi-arrow-left me-1"></i>課題一覧に戻る
+        <i class="bi bi-arrow-left me-1" aria-hidden="true"></i>課題一覧に戻る
     </a>
 </div>
 
 <div class="card shadow-sm">
     <div class="table-responsive">
-        <table class="table table-hover mb-0">
+        <table class="table table-hover mb-0" aria-label="繰り返し設定一覧">
             <thead class="table-light">
                 <tr>
-                    <th class="ps-3">タイトル</th>
-                    <th>科目</th>
-                    <th>繰り返し</th>
-                    <th>状態</th>
-                    <th class="text-end pe-3">操作</th>
+                    <th scope="col" class="ps-3">タイトル</th>
+                    <th scope="col">科目</th>
+                    <th scope="col">繰り返し</th>
+                    <th scope="col">状態</th>
+                    <th scope="col" class="text-end pe-3">操作</th>
                 </tr>
             </thead>
             <tbody>
@@ -38,9 +36,7 @@
                         <span class="text-muted">-</span>
                         {{end}}
                     </td>
-                    <td>
-                        <span class="text-dark">{{recurringSummary .}}</span>
-                    </td>
+                    <td><span class="text-dark">{{recurringSummary .}}</span></td>
                     <td>
                         {{if .IsActive}}
                         <span class="badge bg-success">有効</span>
@@ -49,15 +45,19 @@
                         {{end}}
                     </td>
                     <td class="text-end pe-3">
-                        <a href="/recurring/{{.ID}}/edit" class="btn btn-sm btn-outline-primary">
-                            <i class="bi bi-pencil"></i>
+                        <a href="/recurring/{{.ID}}/edit" class="btn btn-sm btn-outline-primary" aria-label="{{.Title}}を編集">
+                            <i class="bi bi-pencil" aria-hidden="true"></i>
                         </a>
                     </td>
                 </tr>
                 {{else}}
                 <tr>
-                    <td colspan="5" class="text-center py-4 text-muted">
-                        繰り返し設定がありません
+                    <td colspan="5" class="text-center py-5">
+                        <i class="bi bi-arrow-repeat display-4 text-muted" aria-hidden="true"></i>
+                        <p class="mt-2 mb-1 text-muted fw-bold">繰り返し設定がありません</p>
+                        <a href="/assignments/new" class="btn btn-sm btn-primary mt-1">
+                            <i class="bi bi-plus-lg me-1" aria-hidden="true"></i>繰り返し課題を作成する
+                        </a>
                     </td>
                 </tr>
                 {{end}}
@@ -65,4 +65,4 @@
         </table>
     </div>
 </div>
-{{end}}
\ No newline at end of file
+{{end}}