URLからHtmlを取得する関数

Option Explicit
Dim oHttp      As Object

Public Function GetHtmlsource(strURL As String)

  If oHttp Is Nothing Then
    Set oHttp = CreateObject("MSXML2.XMLHTTP")
  End If

  oHttp.Open "GET", strURL, False
  oHttp.setRequestHeader "If-Modified-Since", "Thu, 01 Jun 1970 00:00:00 GMT"
  oHttp.Send

  GetHtmlsource = oHttp.responseText

  If (oHttp.Status < 200 Or oHttp.Status >= 300) Then
    MsgBox "URL読み込みに失敗しました", vbExclamation + vbOKOnly, "Error!"
    GetHtmlsource = ""
  End If

End Function