diff --git a/_pages/time-table.html b/_pages/time-table.html
index 85afbd4..23c2e82 100644
--- a/_pages/time-table.html
+++ b/_pages/time-table.html
@@ -119,31 +119,4 @@ <h2 class="text-4xl text-center mb-8">
       </tbody>
     </table>
   </div>
-
-  <script>
-    // 重複検知（後勝ち）
-    (function () {
-      const data = {
-        slot: {{ slot | jsonify }},
-        dayStart: {{ day_start_min | jsonify }},
-        dayEnd: {{ day_end_min | jsonify }},
-        rooms: {{ rooms | jsonify }},
-        events: {{ tt.events | jsonify }}
-      };
-      const map = new Map();
-      data.rooms.forEach(r => map.set(r, []));
-      const toMin = t => { const [h,m]=String(t).split(':').map(Number); return h*60+m; };
-      for (const ev of data.events) (map.get(ev.room)||map.set(ev.room,[]).get(ev.room)).push(ev);
-      for (const [room, list] of map) {
-        list.sort((a,b)=>toMin(a.start)-toMin(b.start));
-        for (let i=0;i<list.length-1;i++){
-          const a=list[i], b=list[i+1];
-          const as=Math.max(toMin(a.start), data.dayStart);
-          const ae=Math.min(toMin(a.end),   data.dayEnd);
-          const bs=Math.max(toMin(b.start), data.dayStart);
-          if (ae>bs) console.warn(`[time-table] Overlap in "${room}":`, a, b, '→ later wins');
-        }
-      }
-    })();
-  </script>
 </section>
diff --git a/_tests/custom_checks.rb b/_tests/custom_checks.rb
index ff381ef..1fd7082 100644
--- a/_tests/custom_checks.rb
+++ b/_tests/custom_checks.rb
@@ -3,6 +3,7 @@
 
 require 'json'
 require 'yaml'
+require 'time'
 
 class CustomChecks < ::HTMLProofer::Check
   BASE_PATH = '_site'
@@ -10,7 +11,9 @@ class CustomChecks < ::HTMLProofer::Check
   def run
     filename = @runner.current_filename
     puts "\tchecking ... " + filename.delete_prefix('_site')
+
     check_directory_structure(filename) if filename.end_with?('.html')
+    check_time_table_overlaps if filename.end_with?('time-table/index.html')
   end
 
   # Check directory structure to ensure all pages are generated as index.html
@@ -45,4 +48,48 @@ def is_redirect_file?(filename)
     content.include?("<meta http-equiv='refresh'") ||
     content.include?('<meta http-equiv=refresh')
   end
+
+  # Check time table overlaps using Range#cover?
+  def check_time_table_overlaps
+    data = YAML.load_file('_data/time_table.yml')
+
+    # 会議室ごとにイベントをグループ化
+    room_events = Hash.new { |h, k| h[k] = [] }
+
+    data['events'].each do |event|
+      start_time = Time.parse(event['start'])
+      end_time   = Time.parse(event['end'])
+
+      room_events[event['room']] << {
+        title:     event['title'],
+        start_str: event['start'],
+        end_str:   event['end'],
+        range:     (start_time...end_time)  # 終了時間を含まない範囲
+      }
+    end
+
+    # 各会議室で重複チェック
+    room_events.each do |room, events|
+      # 開始時間でソート
+      sorted = events.sort_by { |e| e[:range].begin }
+
+      # 隣接するイベント間で重複をチェック
+      sorted.each_cons(2) do |a, b|
+        # Range#cover? で重複検出
+        if a[:range].cover?(b[:range].begin)
+          add_failure(
+            <<~ERROR_MESSAGE
+              タイムテーブルに重複があります [#{room}]:
+              \s #{a[:start_str]}-#{a[:end_str]}: #{a[:title]}
+              \s #{b[:start_str]}-#{b[:end_str]}: #{b[:title]}
+            ERROR_MESSAGE
+          )
+        end
+      end
+    end
+
+    puts "\t✓ タイムテーブル重複検知完了"
+  rescue => e
+    add_failure("タイムテーブル検証エラー: #{e.message}")
+  end
 end