A plasma electrode is provided with an electrode plate, a ground plate, and an insulating plate arranged between the electrode plate and the ground plate. Protrusions of the electrode plate are arranged inside through holes of the ground plate and inside through holes of the insulating plate. One of the through hole provided on the center axes of the protrusions and the through hole provided around the through hole discharges a first processing gas to below the ground plate. The other of the through holes exhausts a gas existing below the ground plate. A second flow path around the protrusions supplies a second processing gas supplied via a first flow path to a gap between outer walls of the protrusions and inner walls of the through holes. The second processing gas supplied to the gap is converted into plasma by high frequency power applied to the electrode plate.