Abstract: In a CAD system for designing wiring patterns, a wiring start point and a wiring end point are selected from a component placement drawing of a printed wiring board displayed on a display screen using a pointing device. The pointing device is used to designate a point through which the wiring will pass. When this designated point is neither in the horizontal nor vertical direction from the wiring start point, a pattern having two segments is drawn from the wiring start point to the designated point. One of the two segments is a vertical or horizontal segment. The other segment is an oblique segment at a predetermined angle to the horizontal. It can then be determined which of the two segments is to be drawn from the wiring start point. A pattern is similarly drawn from a last designated point to a new designated point.