In plasma processing, damage on a cover is prevented while thermal effect on an annular frame is suppressed. Plasma processing is applied to a substrate held by a carrier including an annular frame and a holding sheet. There are provided a chamber having a decompressible internal space, a plasma source for generating plasma in the chamber, a stage that is provided in the chamber and places the carrier thereon, and a cover that is placed above the stage to cover the holding sheet and the frame, and has a window penetrating through the thickness of the cover. The cover is made of a material having a high thermal conductivity, and a front face exposed to plasma, at least on the side of the window of the cover, is covered with a protect part made of a material having a low reactivity with plasma.