Abstract: There is provided a capacitor having an end connected to the ground and the other end connected through a secondary winding of a pulse transformer to the discharge electrode. The ground side terminal of the capacitor is connected through a smoothing circuit to a positive voltage side output terminal of a base power supply circuit and a negative voltage side terminal of the base power supply circuit is connected to the discharge electrode side terminal of the capacitor. An output terminal of a pulse power supply circuit is connected to a primary winding of the pulse transformer. The base voltage and the pulse voltage can be controlled independently, and it becomes possible to apply a steep pulse with large output power to the discharge electrode.