PURPOSE: To efficiently consume making electric power for interpole gap discharging machining by returning a part of the electric power to a DC power source at the time of turn-off by a rectifier coupled with a transformer instead of a resistor for consuming electric power.

CONSTITUTION: In a power source device for pulse discharge between an electrode 1 and a workpiece to process the workpiece, semiconductor switching elements 9aW9d, a transformer 13, a control device 14, rectifiers 15a, 15b, a choke coil 16 and a condenser form a intermittently operating high-frequency inverter in which input voltage is contrived to be a constant voltage. The inverter is adapted to convert from AC to DC in such a manner as to keep the voltage of a condenser 7 at a reference value. A DC output thus returned to a DC power source is loaded on the DC power source to be a constant voltage, and again becomes a voltage supply source to the interpole gap 3. Thus, making electric power is efficiently consumed for interpole gap discharge machining.