A plasma processing apparatus composed of a processing chamber in a vacuum vessel to which a gas is fed to form a plasma, a sample stage in which a channel for a heat exchange medium is formed, beams for supporting the sample stage in the horizontal direction, a cylindrical space at atmospheric pressure formed below the channel in the sample stage, coupling paths for communicating the inner wall of the cylindrical space with the exterior of the vacuum vessel, a piping conduit for medium formed in the coupling path, a drive mechanism to drive pins for a wafer, and metal blocks covering junctions between the piping conduits for medium and the sample stage, whereby a gas at high temperature is supplied to between the metal blocks and is exhausted through the coupling path.