PURPOSE: To relax the one sided distribution of monocrystal powder of Si in working fluid, and thereby lessen dimensional errors during machining a work by disposing an exciter in working fluid to vibrate the working fluid so as to stir it.

CONSTITUTION: A work 4 is rested on working fluid 2, and concurrently machining the work 4 is started with electric discharge machining carried out between the work 4 and an electrode 8 within the working fluid 2 in a state that monocrystal powder 3 of Si is floated. In this case, an exciter 5 is provided in the working fluid 2 to stir the working fluid 2 with vibration applied. This constitution thereby allows monocrystal powder 3 of Si to be stirred within the working fluid 2 with the vibration of the exciter 5 transmitted to the working fluid 2, the one sided concentration is thereby relaxed between the work 4 and the electrode 8 and the like so as to be uniformed and machining speed on the work 4 is then uniformed so that dimensional errors in machining sections can thereby be downsized.