An elastic coupling, wherein drive side and driven side collars can be press fitted easily, securely and firmly to inner cylinder members with a sufficient interference and which can be used without a danger of axial deviation or disconnection and can be enhanced in durability and reliability. An eliminating airflow is ejected from a row of air nozzles when the detected foreign substance falls down, and deflects the falling direction of the foreign substance. In addition, channel widths and gate widths for the first transistor are larger than those of the second transistor. The integrator circuit responsive to the error signal and configured for computing the output signal. In accordance with the invention the bed is not only worked on in pulses by the hammers but is also subjected to compression. The apparatus includes a processing having an open upper part, a hot plate disposed in the chamber and on which a wafer is to be mounted, a cover covering the upper part of the chamber; and a thin film made of material having a low emissivity extending over the inner surface of the cover.