Disclosed is a plasma processing device that provides an object to be treated with plasma treatment. A wafer as an object to be treated, which is attached on the upper surface of adhesive sheet held by a holder frame, is mounted on a stage. In a vacuum chamber that covers the stage therein, plasma is generated, by which the wafer mounted on the stage undergoes plasma treatment. The plasma processing device contains a cover member made of dielectric material. During the plasma treatment on the wafer, the holder frame is covered with a cover member placed at a predetermined position above the stage, at the same time, the wafer is exposed from an opening formed in the center of the cover member.