An electric-discharge-machining power supply device in which energy loss is hardly produced and a charge voltage of a capacitor is easily controlled. When a switching element SW1 is turned on, a capacitor C is charged via an inductor L. When the voltage Vc of the charged capacitor exceeds the voltage of a direct-current power source E, a current is returned to the power source E via a diode D2. When the switching element SW1 is turned off, energy stored in the inductor L flows from the inductor L through the diode D2, the power source E and the diode D1, so that the voltage Vc of the capacitor C is kept at the power source voltage. When a switching element SW2 is turned on, the voltage of the capacitor is applied between an electrode and a workpiece.