ComboBox.ItemsにObjectをセットしている場合のIndexOf

Public Class ItemList
        Private mItemVal As String '名称
        Private mIDVal As String 'コード

        Public Property ItemVal() As String
            Get
                Return mItemVal
            End Get

            Set(ByVal sValue As String)
                mItemVal = sValue
            End Set
        End Property

        Public Property IDVal() As String
            Get
                Return mIDVal
            End Get

            Set(ByVal iValue As String)
                mIDVal = iValue
            End Set
        End Property
        Public Overrides Function ToString() As String
            Return mItemVal
        End Function
    End Class

For cnt As Integer = 0 To Me.ComboBox1.Items.Count - 1
	If cboCONSTR_KBN.Items(cnt).itemval = ターゲット文字列 Then
		cboCONSTR_KBN.SelectedIndex = cnt
	End If
Next