The object of the present invention is to provide a plasma processing apparatus capable of processing a substrate stably for a long period of time. The plasma processing apparatus has a substrate holder disposed in a processing chamber and an electrode cover for protecting a support stage of said substrate holder, for processing a wafer placed on said support stage using a plasma generated in the processing chamber, wherein at least a surface of said electrode cover that is positioned directly below an edge of the wafer, or at least a surface of said electrode cover that comes into contact with plasma, is coated with a material having resistance to plasma and comprising Y2O3, Yb2O3 or YF3, or a mixture thereof, as its main component.