diff --git a/db/migrate/20220415193829_add_index_for_question_id_index_on_inboxes.rb b/db/migrate/20220415193829_add_index_for_question_id_index_on_inboxes.rb
new file mode 100644
index 00000000..63ef74c7
--- /dev/null
+++ b/db/migrate/20220415193829_add_index_for_question_id_index_on_inboxes.rb
@@ -0,0 +1,5 @@
+class AddIndexForQuestionIdIndexOnInboxes < ActiveRecord::Migration[6.1]
+  def change
+    add_index :inboxes, :question_id
+  end
+end