A substrate processing apparatus includes: a depressurizable processing chamber 11; a shaft 26 supporting a facing electrode 24 provided within the processing chamber 11 while allowing the facing electrode 24 to be movable with respect to a mounting electrode 12; a first ring-shaped bellows 31 concentrically installed at an outer peripheral portion of the shaft 26; and a second bellows 32 concentrically installed at an outer peripheral portion of the first bellows 31. The first bellows 31 absorbs a displacement of the facing electrode 24 with respect to a wall surface 13 at a penetration portion where the shaft 26 penetrates the wall surface 13 of the processing chamber 11, and seals the inside of the processing chamber 11 against the ambient atmosphere around the shaft 26. A ring-shaped gas flow path 35 is formed by the first bellows 31 and the second bellows 32.