Sub TEST()
Dim i As Long, n As Long, dic As Object, D
n = Cells(Rows.Count, 1).End(xlUp).Row
D = Range("A4", Cells(n, 2)).Value
Set dic = CreateObject("Scripting.Dictionary")
For i = 1 To UBound(D)
If dic.exists(D(i, 1)) Then
If dic(D(i, 1)) > D(i, 2) Then
dic(D(i, 1)) = D(i, 2)
End If
Else
dic(D(i, 1)) = D(i, 2)
End If
Next
For i = 4 To n
If Cells(i, 2) = dic(Cells(i, 1).Value) Then
Cells(i, 4) = "○"
End If
Next
End Sub
お試しください。