Creer menu deroulant avec choix multiple

Private Sub Worksheet_Change(ByVal Target As Range)

'Code by Sumit Bansal from www.trumpexcel.com
' To Select Multiple Items from a Drop Down List in Excel

Dim Oldvalue As String
Dim Newvalue As String

On Error GoTo Exitsub
If Target.Address = "$R$5" Then
    If Target.SpecialCells(xlCellTypeAllValidation) Is Nothing Then
    GoTo Exitsub
    Else: If Target.Value = "" Then GoTo Exitsub Else
        Application.EnableEvents = False
        Newvalue = Target.Value
        Application.Undo
        Oldvalue = Target.Value
        If Oldvalue = "" Then
            Target.Value = Newvalue
        Else
            Target.Value = Oldvalue & ", " & Newvalue
        End If
    End If
End If
Application.EnableEvents = True

Exitsub:
Application.EnableEvents = True

End Sub