Option Strict On Public Class Form1 Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load Dim plus As New TreeNodePlus plus.CustomMessage = "本日は晴天なり" TreeView1.Nodes.Add(plus) End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim plus As TreeNodePlus = TreeView1.FindTreeNodePlus(0) MsgBox(plus.CustomMessage) End Sub End Class Public Module TreeViewExtender <Runtime.CompilerServices.Extension> Public Function FindTreeNodePlus(source As TreeView, index As Integer) As TreeNodePlus Dim node = source.Nodes(index) Return DirectCast(node, TreeNodePlus) End Function End Module Public Class TreeNodePlus Inherits TreeNode Public Property CustomMessage As String Public Sub New() Me.Text = Now.ToString End Sub End Class