PURPOSE: To reduce charge-up damage on a processed substrate by performing plasma processing of a substrate to be processed while protecting the underside and the peripheral part of the processed substrate where an insulating film is formed on the conductive base plate from plasma.

CONSTITUTION: Plasma processing of a substrate S to be processed is performed while protecting the underside and the peripheral part of a processed substrate S having a insulating film on a conductive base plate from a plasma by a peripheral ring 15. The peripheral ring 15 is made of alumina and can be divided in two. At the time of placing the processed substrate S on an electrostatic chuck 25, the peripheral ring 15 is opened and the substrate S to be treated is placed on the electrostatic chuck 25 followed by closing the peripheral ring 15. Here, due to a structure where the peripheral ring 15 comes in contact with the peripheral part of the substrate S to be processed, the peripheral part of the processed substrate S and the surface peripheral part can be prevented from being exposed to plasma during plasma processing.