PURPOSE: To perform accurate machining of a work even for a change of material and rapid change of plate thickness, by storing an electric machining condition in a memory and selectively changing the electric machining condition on the basis of contents of the machining condition.

CONSTITUTION: Positions of all switching points on a machining route, electric machining condition and switching modes are stored in a memory M1, and then a wire electrode P is extensibly mounted in a running system to start electric discharge machining. A control device CPU, referring to the memory M1, discriminates which of the switching modes A, B, C has been set. When the switching mode A is decided to be set, a position of the switching point, stored in the memory M1, and position from a detecting result of detectors PCX, PCY are compared, if the both are agreed, control signals a1Wan, b1Wbn, c1Wcn, d1W dn are applied to a control unit EC through an output device DO, and the electric machining condition is switched.