A phase of the pulse control signal upon restarting is synchronized with the phase of the pulse control signal upon suspending, thereby suppressing fluctuations of output voltage in each phase of the inverter upon restarting and further suppressing fluctuations of voltage supplied to the load. Upon supplying DC power to a plasma generator, when arc discharge occurs in the plasma generator, supplying of the DC power is suspended to reduce damage on the electrodes and substrate, and further upon extinguishing of the arc discharge, supplying of the DC power is restarted. In suspending and resuming the DC output, the current flowing in the chopper upon suspending is held in the form of circulating current, and upon restarting the inverter, this circulating current is supplied to the load. Accordingly, it is possible to reduce a delay in supplying the DC power to the load, upon resuming the DC output.