A power supply device for wire electric discharge machining includes: a first DC power supply; first switching elements between the first DC power supply and a machining gap; a second DC power supply; a second switching element between the second DC power supply and the machining gap; and a pulse generator controlling the first and second switching elements. The pulse generator is configured so that, in order to generate an electric discharge in the machining gap, the second switching element is switched on and the voltage of the second DC power supply is applied to the machining gap; the first switching element is switched on intermittently at a predetermined frequency in response to an electric discharge generation detection signal, and a series of current pulses is fed to the machining gap. The feeding of the series of current pulses is discontinued when the current pulses don't reach a reference current.