Sub nenkan_5gatsu_ok()
    Dim d As Date
    Dim c As Long
    d = #1/1/2015#
    c = 2
    
    Do While Year(d) = 2015
        If Month(d) = 5 Then
            Range("A" & c).Value = d
            Range("B" & c).Value = WeekdayName(Weekday(d), True)
            c = c + 1
        End If
        d = DateAdd("d", 1, d)
        Debug.Print d
    Loop
End Sub
Sub nenkan_5gatsu_ng()
    Dim d As Date
    Dim c As Long
    d = #1/1/2015#
    c = 2
    
    Do While Year(d) = 2015
        If Month(d) = 5 Then
            Range("A" & c).Value = d
            Range("B" & c).Value = WeekdayName(Weekday(d), True)
            c = c + 1
            d = DateAdd("d", 1, d)
        End If
        Debug.Print d
    Loop
End Sub