PURPOSE: To prevent the occurrence of new violation wiring owing to the correction of violation wiring.

CONSTITUTION: Current wiring information is stored in a wiring information storage means 1. A wiring state display means 2 displays a current wiring state by using this information. Here, a designer designates wiring being a correction object. A wiring length calculation means 3 obtains a current wiring length for the designated wiring, and an allowance wiring length calculation means 4 calculates an allowance wiring length. Furthermore, a wiring length margin degree display means 5 displays the ratio of the obtained current wiring length and the allowance wiring length (current wiring length/allowance wiring length ×10). The designer does not come to select wiring with little margin degree of the wiring length and recognizes the margin degree of a noticed wiring route so as to alter the route. At the time of correction, a wiring route correction means 6 corrects designated wiring.