A power supplying device for an electric discharge machine prevents electric discharge by a voltage from a subsidiary power supply circuit during a delay time from generation of the electric discharge to a rise of a voltage from a main power supply circuit. A parallel circuit, of a current reducing resistor and a capacitor, is provided in series in the subsidiary power supply circuit. A controller turns on the subsidiary power supply circuit to apply a voltage between a first electrode and a workpiece, as a second electrode, to generate an electric discharge therebetween, electricity charging the capacitor flowing between the electrodes to maintain the electric discharge even if an electric discharge current oscillates. The controller further turns on a main power supply circuit to supply a machining current in response to detection of the electric discharge and the current reducing resistor suppresses any leakage current during the application of the voltage from the subsidiary power supply circuit.