diff --git a/VQCalendarAttention/Services/NextDayCalendarAttentionService.cs b/VQCalendarAttention/Services/NextDayCalendarAttentionService.cs
index b26bf08..3a62648 100644
--- a/VQCalendarAttention/Services/NextDayCalendarAttentionService.cs
+++ b/VQCalendarAttention/Services/NextDayCalendarAttentionService.cs
@@ -60,7 +60,13 @@
             DateTime startOfTomorrow = jst.Date.AddDays(1);
             DateTime endOfTomorrow = startOfTomorrow.AddDays(1);
 
-            var tomorrowEvents = events.Items.Where(e => e.Start.DateTime >= startOfTomorrow && e.Start.DateTime < endOfTomorrow).ToList();
+            var tomorrowEvents = events.Items.Where(
+                e => (e.Start.DateTime.HasValue && 
+                    e.Start.DateTime >= startOfTomorrow && e.Start.DateTime < endOfTomorrow) ||
+                    (e.Start.Date != null && 
+                        DateTime.Parse(e.Start.Date).Date == startOfTomorrow.Date
+                    )
+                ).ToList();
             // 明日の予定を表示
             if (tomorrowEvents.Count > 0)
             {
@@ -81,7 +87,8 @@
                     {
                         importanceMention = $" <@&{roleId}>";
                     }
-                    sb.AppendLine($"{tomorrowEvent.Summary}: {tomorrowEvent.Start.DateTime}{importanceMention}");
+                    string startTime = tomorrowEvent.Start.DateTime?.ToString("yyyy-MM-dd HH:mm:ss") ?? DateTime.Parse(tomorrowEvent.Start.Date).ToString("yyyy-MM-dd");
+                    sb.AppendLine($"{tomorrowEvent.Summary}: {startTime}{importanceMention}");
                 }
 
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