diff --git a/dictation_client/src/App.tsx b/dictation_client/src/App.tsx
index 1d47893..f08dfd1 100644
--- a/dictation_client/src/App.tsx
+++ b/dictation_client/src/App.tsx
@@ -43,14 +43,18 @@ const App = (): JSX.Element => {
 
   // Language読み取り
   useLayoutEffect(() => {
-    const language = document.cookie
-      .trim()
-      .split(";")
-      .map((x) => x.split("="))
-      .find((x) => x.length === 2 && x[0] === "language");
+    const { cookie } = document;
 
-    if (language) {
-      i18n.changeLanguage(language[1]);
+    if (cookie) {
+      const cookieArray = cookie.split(";");
+      const language = cookieArray.find((x) =>
+        // 先頭の空白を削除してから判定
+        x.trim().startsWith("language=")
+      );
+
+      if (language) {
+        i18n.changeLanguage(language.split("=")[1]);
+      }
     }
   }, [i18n]);