Check If Cells Contains Only Numbers

how to check if cells contain only whole numbers (cells are in text format)?

I do not know how the code is for the activecell checking

Example Range("A1:A10")

ColumnA
12345
12345
555,10
12345
1.20
A6666
12345
12345
12345

As soon the code hits a cell containing something other then numbers then Msgbox "Error"

Sub Check()

i = 1
Do Until Cells(i, 1).Text = ""
Cells(i, 1).Select

If Not Activecell.Text only numbers then
MsgBox "Error"
End If

i = i + 1

Loop

End Sub