In a plasma processing apparatus including a processing chamber in a vacuum container to form plasma in the processing chamber in which pressure is reduced, a sample stage in lower part of inside of the processing chamber and having an upper surface on which a wafer to be processed by plasma is put, a plurality of pins in the sample stage to be moved in vertical direction so that the pins abut against rear side of the wafer to move the wafer up and down over the upper surface of the sample stage, and a plurality of openings formed in the upper surface of the sample stage so that the pins are moved in the openings, gas is fed from supply ports communicating with the openings into the processing chamber through the openings when the wafer is not put on the upper surface of the sample stage.