A designing method of a semiconductor device is achieved by setting interconnection reference data indicating permissible interconnection widths which are discrete, and a permissible interval between adjacent two of interconnections, the interconnection intervals being discrete; and by specifying an interconnection relating an impermissible width and interconnections relating to an impermissible interval from the interconnections for a semiconductor device based on the interconnection data. The permissible widths and the permissible intervals are preferably equal to or larger than a minimum design dimension.