The present invention is equipped with a series circuit that includes a DC power supply, switching elements and a diode for supplying DC or AC current pulses to a machining gap between a machining electrode and a workpiece, diodes that regulate a direction of the current flow to one direction, and a control unit that controls the switching elements. When the control unit generates a current pulse having a triangular waveform by an inductance that is present in the series circuit, the control unit controls the switching elements in order that a current-pulse time ratio that is a ratio between the non-current time and the current continuation time in the current pulse is equal to or lower than ⅕.