PURPOSE: To efficiently discharge the electric charges of condensers by installing an electric discharge part in which a plurality of electric discharge switches for condensers for electrically discharging the electric charges charged between a workpiece and an electrode and a control part for controlling the electric discharge of the electric charges of the condensers.

CONSTITUTION: All or a part of the electric discharge switches 30-1W30-n connected in parallel in an electric discharge part 31 are selectively turned-ON/OFF by the control signals of a controller 11, electric charge/discharge control part 25, etc. For example, in case of the relatively low electric current density of the pulse such as in finishing work, the electric discharge switches 30-1W30-10 are turned ON, and when the electric discharge current becomes less than the min. current value during the electric discharge machining these switches 30-1W30-10 are turned-OFF immediately, and the electric discharge supplied from condensers 28-1W28-n is suspended. Therefore, the number of used condensers 28-1W28-n is properly controlled according to the current density of the supplied pulse, and the charges of the condensers 28-1W28-n can be discharged efficiently.