A spring member (23) is confined between a back pressure sealing band (21) and a ring groove (22) formed in a bearing member (18) housing this back pressure sealing band (21) so as to constantly press the back pressure sealing band (21) against the rear surface of a revolving mirror plate (11). The back pressure sealing band (21) is constantly pressed against the rear surface of the revolving mirror plate (11) by the spring member (23) irrespective of the conditions immediately after the start or the operating conditions, the thrust force applied in the axial direction to the revolving mirror plate (11) of the revolving scroll from a space for the compression works can be relieved due to the discharge pressure of a compressor mechanism acting on the center of the revolving mirror plate (11) and a suitable intermediate pressure between a discharge pressure acting on the outer portion of the plate and an intake pressure, whereby the power loss due to the sliding and the like made on the planar surface of the revolving mirror plate (11) is reduced, thus improving the working efficiency of the compressor.
