PURPOSE: To prevent lowering of machining accuracy by repeating a process of making a pair of wire guides move in the forward direction relatively to a work to be machined and a process of making it move to the opposite direction cyclically.

CONSTITUTION: A wire electrode 3 stretched between a pair of wire guides 5, 5' is opposed to a work to be machined 4 with a predetermined machining clearance. Electrical discharge is made to generate by applying intermittent machining voltage pulse between the wire electrode 3 and the work 4 while supplying machining liquid to the machining clearance from a machining liquid injection nozzle. And the pair of wire guides 5, 5' are made to go oppositely to the work to be machined 4 relatively. During the time, the machining clearance is opened and gas and sludge etc. are rapidly removed, and machining performance is improved.