【VBA】結合されたセルを配列を使って高速に削除する方法

Option Explicit
Sub UnmergeCells()
    Dim ws As Worksheet
    Set ws = ThisWorkbook.Sheets("Sheet1")
    Application.ScreenUpdating = False
    Dim lastRow As Long, i As Long
    lastRow = ws.Cells(ws.Rows.Count, "A").End(xlUp).Row
    Dim rng As Range
    For i = 1 To lastRow
        If Not IsEmpty(ws.Range("A" & i)) Then
            If ws.Range("A" & i).MergeCells Then
                If rng Is Nothing Then
                    Set rng = ws.Range("A" & i)
                Else
                    Set rng = Union(rng, ws.Range("A" & i))
                End If
            End If
        End If
    Next i
    If Not rng Is Nothing Then rng.UnMerge
    Application.ScreenUpdating = True
End Sub