PURPOSE: To prevent the disconnection between a land and s strip in forming a pattern for automatic designing of a wiring pattern of a printed circuit board by detecting the juncture between the strip and land and expanding the shape of the land in the direction of the strip.

CONSTITUTION: A circuit diagram is inputted and the parts to be used are disposed. The juncture between a strip and a land, that is, in which part of the land the strip is connected is detected, then the shape of the land is expanded in the direction of the strip. Automatic wiring is accomplished by using the shape data on the expanded land. The juncture of the strip and the land is detected and the shape of said land is expanded in the direction of said strip in the above-mentioned way and therefore even if the position of a through- hole deviates in the stage of punching the hole, the disconnection between the land and the strip is obviated. The quality of the printed circuit board and the density of wiring are thus improved.