Abstract: In a plasma processing apparatus for conducting plasma process on a semiconductor wafer 5, a lower electrode 3 provided with an electrode member 46 is disposed in a bottom part 40c of a chamber container 40 which is a main body of a vacuum chamber 2, and an upper electrode 4 provided with a projected face which is projected downward from its lower face inward of its outer edge portion 51a lower than a lower face of the outer edge portion is disposed above the lower electrode 3 so as to move up and down. The upper electrode 4 is moved downward toward the lower electrode 3 to bring the outer edge portion 51a into contact with an annular hermetically sealing face 40d which is formed at an intermediate level HL in a side wall part 40a of the chamber container 40, whereby a hermetically sealed process space 2a is formed between the lower electrode 3 and the upper electrode 4.