The active workbook, replace the contents of the H13 cell in all worksheets

Sub J3v16()
Dim ws As Worksheet
For Each ws In ThisWorkbook.Sheets
    With ws
        .Cells.Replace what:="https://www.hitachi.co.jp/", Replacement:="https://www.casio.com/jp/", _
        LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, _
        SearchFormat:=False, ReplaceFormat:=False
    End With
Next ws
End Sub