A method includes: before carrying out a timing verification processing of a semiconductor circuit, preliminarily superposing and arranging a dummy pattern template representing an arrangement pattern of dummy metal, onto a layout area defined by layout data while changing an origin position of the dummy pattern template to optimize the origin position of the dummy pattern template; and upon detecting that the result of the timing verification processing has no problem, superposing and arranging the dummy pattern template onto the layout area at the origin position of the dummy pattern template, to generate the layout data after inserting the dummy metal.