Abstract: An intermediate body 19 is interposed between the hot plate 17 and the stage 18. The contact surfaces of the hot plate 17 and intermediate body 19 are less than 10 nm in surface roughness. The hot plate 17 and the intermediate body 19 are directly contacted with each other. Secure sealing can be obtained between the hot plate 17 and the intermediate body 19 without using heat-endurable seal material. The heat transfer gas is prevented from leaking from the contact surfaces of the hot plate 17 and intermediate body 19. The result is that the construction is simplified, the manufacturing cost is low, the maintenance is good and sealability of the heat transfer gas can be secured.