PURPOSE: To reduce the number of unused wires by a method wherein a wiring width of a bundle-shaped connection (bundled wires) between circuit elements is computed and, when a wiring region is narrower than the wiring width of the bundled wires, the bundled wires are divided and wired in parallel.

CONSTITUTION: A bundled-wires detection means 1 takes out a piece of connection information from a design data base 7, detects bundled wires between circuit elements and stores this information in a bundled-wires table 8. A wiring- model formation means 2 takes out a piece of arrangement information of a circuit element from the data base 7 and constructs a wiring model in a working region 9. A wiring-region search means 4 searches, on the working area 9, a vacant region of a wiring width computed by a wiring-width computation means 3 from the table 8. When a wiring region satisfying the wiring width cannot be obtained, a bundled-wires division means 5 divides the bundled wires and registers this information again in the table 8. A route decision means 6 decides a wiring route in the wiring region obtained in the working area 9 and writes it in the data base 7.