A processing system has an upper electrode with gas discharge holes of a shape corresponding to the external we of insulating members. The insulating members are formed of a poly(ether etherketone) resin, a polyimide resin, a poly(ether imide) resin or the like. Each insulating member has a step at its outer surface and an internal longitudinal through hole tapered to expand toward the processing chamber. The insulating members are pressed in the gas discharge holes to bring the steps into contact with shoulders formed in the sidewalls of the gas discharge holes. A part of each insulating member, as fitted in the gas discharge hole, projects from a surface of the upper electrode that faces a susceptor.