diff --git a/data_migration_tools/server/src/features/transfer/transfer.service.ts b/data_migration_tools/server/src/features/transfer/transfer.service.ts
index 8168c04..b229a51 100644
--- a/data_migration_tools/server/src/features/transfer/transfer.service.ts
+++ b/data_migration_tools/server/src/features/transfer/transfer.service.ts
@@ -511,7 +511,7 @@ export class TransferService {
       // accountsFileLinesの行ループ
       accountsFileLines.forEach((account) => {
         const duplicateAdminMail = newAccountsFileLines.find(
-          (a) => a.adminMail === account.adminMail
+          (a) => a.adminMail.toLowerCase() === account.adminMail.toLowerCase() // メールアドレスは大文字小文字を区別しない
         );
 
         if (duplicateAdminMail) {
@@ -531,7 +531,7 @@ export class TransferService {
       // usersFileLinesの行ループ
       usersFileLines.forEach((user) => {
         const duplicateUserEmail = newUsersFileLines.find(
-          (u) => u.email === user.email
+          (u) => u.email.toLowerCase() === user.email.toLowerCase() // メールアドレスは大文字小文字を区別しない
         );
 
         if (duplicateUserEmail) {
@@ -553,7 +553,7 @@ export class TransferService {
         }
         // newAccountsFileLinesとの突合せ
         const duplicateAdminUserEmail = newAccountsFileLines.find(
-          (a) => a.adminMail === user.email
+          (a) => a.adminMail.toLowerCase() === user.email.toLowerCase() // メールアドレスは大文字小文字を区別しない
         );
         // 重複がある場合
         if (duplicateAdminUserEmail) {