<p>There is provided a capacitor (20) having an end connected to the ground and the other end connected through a secondary winding of a pulse transformer (16) to the discharge electrode (41). The ground side terminal of the capacitor (20) is connected through a smoothing circuit (25) to a positive voltage side output terminal of a base power supply circuit (30) and a negative voltage side terminal of the base power supply circuit (30) is connected to the discharge electrode side terminal of the capacitor (20). An output terminal of a pulse power supply circuit (30) is connected to a primary winding of the pulse transformer (16). 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 (41). <IMAGE></p>
