diff --git a/app/islands/counter.tsx b/app/islands/counter.tsx
index 41f80273..ce7f5799 100644
--- a/app/islands/counter.tsx
+++ b/app/islands/counter.tsx
@@ -31,7 +31,9 @@ export default function Counter(props: InitialTime) {
         (Number(nextBirthday) - Number(now)) / 1000
       );
       const days = Math.floor(diffInSeconds / (60 * 60 * 24));
+      // hoursを日本時間の24時間計算になるようにする
       const hours = Math.floor((diffInSeconds / (60 * 60)) % 24) - 9;
+      hours < 0 ? hours + 24 : hours;
       const minutes = Math.floor((diffInSeconds / 60) % 60);
       const seconds = diffInSeconds % 60;
 
diff --git a/app/routes/index.tsx b/app/routes/index.tsx
index 842a4165..d716a014 100644
--- a/app/routes/index.tsx
+++ b/app/routes/index.tsx
@@ -13,7 +13,9 @@ export default function Index() {
 
   const diffInSeconds = Math.floor((Number(nextBirthday) - Number(now)) / 1000);
   const days = Math.floor(diffInSeconds / (60 * 60 * 24));
+  // hoursを日本時間の24時間計算になるようにする
   const hours = Math.floor((diffInSeconds / (60 * 60)) % 24) - 9;
+  hours < 0 ? hours + 24 : hours;
   const minutes = Math.floor((diffInSeconds / 60) % 60);
   const seconds = diffInSeconds % 60;