Abstract: In addition to the block placement information and the logical connection information of an LSI, there are disposed a bus name list and a signal name list belonging to each of bus signals as input data. A processing consisting of the two following steps is executed as a method for searching a path for each of the bus signals. (1) A routing area, throgh which the bus signals pass, is determined by gathering all the signals in the bus signals, considering them as a virtual signal representing the bus signals, and searching the path for this virtual signal (2). For each of the signals in the bus signals the path is searched within the routing area for the bus signals obtained at Step (1).