' ワークブックを開く時のイベント
Private Sub Workbook_Open()
    Dim path As String
    Dim filename As String

    path = "C:\Users\【username】\Desktop\test\test1\"
    filename = "新しいテキスト ドキュメント.txt"

    path = path_check(path, filename)

    If path = "" Then
        MsgBox "patherror"
        Exit Sub
    End If

    filepath = path + filename
    n = FreeFile
    Open filepath For Input As #n

    Do While Not EOF(n)
        i = i + 1
        Line Input #n, txtLine
        Cells(i, 1).Value = txtLine
    Loop

    Close #n

End Sub

Option Explicit


Public Function path_check(path, filename)

    Dim i As Integer
    Dim pathflg As Integer
    Dim open_result As Boolean
    Dim FSO As Object
    Dim TextFile As Object
    pathflg = 0

    For i = 0 To 3
        open_result = True
        On Error GoTo ErrLabel
        Set FSO = CreateObject("Scripting.FileSystemObject")
        Set TextFile = FSO.OpenTextFile(path + filename)

        If open_result = True Then
            GoTo success
        End If

    Next i

ErrLabel:
    open_result = False
    Select Case pathflg
        Case 0
            path = "C:\Users\【username】\Desktop\test\test2\"
        Case 1
            path = "C:\Users\【username】\Desktop\test\test3\"
        Case 2
            path = ""
        Case Else
            path_check = ""
    End Select
    pathflg = pathflg + 1
    Resume Next

success:
    path_check = path

End Function