Sub Sample()
Dim fName As String
fName = "test.xlsx"
If IsOpenBook(fName) Then
'処理
End If
End Sub
Function IsOpenBook(ByVal bookName As String) As Boolean
Dim res As Boolean
Dim wb As Workbook
For Each wb In Workbooks
If wb.Name = bookName Then
res = True
Exit For
End If
Next
IsOpenBook = res
End Function