diff --git a/app/models/regular_event.rb b/app/models/regular_event.rb
index 0689f9447b9..e96fbc5f1da 100644
--- a/app/models/regular_event.rb
+++ b/app/models/regular_event.rb
@@ -167,11 +167,8 @@ def nth_wday(date)
   end
 
   def parse_event_time(event_date, event_time)
-    tz = ActiveSupport::TimeZone['Asia/Tokyo']
-
-    time = event_time ? event_time.strftime('%H:%M') : '00:00'
-    date_time = DateTime.parse("#{event_date} #{time}")
-
-    tz.local_to_utc(date_time)
+    str_date = event_date.strftime('%F')
+    str_time = event_time.strftime('%R')
+    Time.zone.parse([str_date, str_time].join(' '))
   end
 end
diff --git a/test/models/regular_event_test.rb b/test/models/regular_event_test.rb
index cc138367e0b..a63ccbe0e5c 100644
--- a/test/models/regular_event_test.rb
+++ b/test/models/regular_event_test.rb
@@ -136,13 +136,15 @@ class RegularEventTest < ActiveSupport::TestCase
     assert_equal wednesday_for_year, scheduled_dates
   end
 
-  test '#format_event_date' do
+  test '#transform_for_subscription' do
     travel_to Time.zone.local(2024, 8, 5, 23, 0, 0) do
-      regular_event = regular_events(:regular_event34)
+      regular_event = RegularEvent.new(start_at: '21:00', end_at: '22:00')
       event_date = Date.new(2024, 8, 7)
       transformed_regular_event = regular_event.transform_for_subscription(event_date)
-      assert_equal DateTime.new(2024, 8, 7, 21, 0, 0, '+09:00'), transformed_regular_event.start_on
-      assert_equal DateTime.new(2024, 8, 7, 22, 0, 0, '+09:00'), transformed_regular_event.end_on
+
+      assert_equal Time.zone.parse('2024-08-07 21:00'), transformed_regular_event.start_on
+      assert_equal Time.zone.parse('2024-08-07 22:00'), transformed_regular_event.end_on
+      assert_equal 'JST', transformed_regular_event.start_on.zone, 'タイムゾーンが日本標準時(Japan Standard Time)と異なります'
     end
   end