A wiring pattern determination method and a computer program thereof comprise a step of moving positions of tentatively designed plated leads on an edge of a semiconductor package to the positions that can be accommodated in positionable windows nearest to the respective tentatively designed plated lead positions, in a template in which the positionable windows are arranged, so that the positionable windows have a predetermined pitch in a row direction corresponding to an identical layer of a multi-layered structure and so that the positionable windows are positioned at least in every other row in a column direction corresponding to a lamination direction of the multi-layered structure and, then, determining the moved positions as optimal positions of the plated leads.