diff --git a/vba_code_kukan_detail_master.txt b/vba_code_kukan_detail_master.txt
index a275bbd..21b3624 100644
--- a/vba_code_kukan_detail_master.txt
+++ b/vba_code_kukan_detail_master.txt
@@ -1,5 +1,6 @@
 ' CSV Header Constants
 Const CSV_HEADER As String = "利用区間コード,券種,コード,名称,1箇月運賃/販売額,定期額/券１(額)/利用額,定期支給期間/券１(枚)/特別料金,特別料金/券２(額),券２(枚),端数(額),特別料金"
+Const CSV_HEADER_ARRAY As Variant = Array("利用区間コード", "券種", "コード", "名称", "1箇月運賃/販売額", "定期額/券１(額)/利用額", "定期支給期間/券１(枚)/特別料金", "特別料金/券２(額)", "券２(枚)", "端数(額)", "特別料金")
 
 Private Sub Worksheet_Change(ByVal Target As Range)
     ' === Generate F dropdown based on G column (matching left of colon) ===
@@ -176,8 +177,20 @@ Sub ImportMasterDetailData()
     If UBound(lines) >= 0 And Trim(lines(0)) <> "" Then
         Dim csvHeader As String
         csvHeader = Trim(lines(0))
-        If csvHeader <> CSV_HEADER Then
-            MsgBox "CSV header mismatch." & vbCrLf & "Expected: " & CSV_HEADER & vbCrLf & "Got: " & csvHeader, vbExclamation
+        ' Validate header by comparing each field
+        Dim headerFields As Variant
+        headerFields = Split(csvHeader, ",")
+        Dim headerMismatch As Boolean
+        headerMismatch = False
+        Dim k As Long
+        For k = 0 To UBound(CSV_HEADER_ARRAY)
+            If k > UBound(headerFields) Or Trim(headerFields(k)) <> CSV_HEADER_ARRAY(k) Then
+                headerMismatch = True
+                Exit For
+            End If
+        Next k
+        If headerMismatch Or UBound(headerFields) <> UBound(CSV_HEADER_ARRAY) Then
+            MsgBox "CSV header mismatch.", vbExclamation
             Exit Sub
         End If
     End If
@@ -383,7 +396,7 @@ Sub ExportMasterDetailData()
     
     ' Use constant for header
     Dim headerList As Variant
-    headerList = Split(CSV_HEADER, ",")
+    headerList = CSV_HEADER_ARRAY
     
     ' Build CSV
     Dim csvContent As String