Disclosed is a compressor which has a fixed scroll and a movable scroll. Defined between both scrolls is a compression chamber in order to provide compressed gas. A pressure receiving member receives compression reaction force of the compressed gas. A base plate is provided on the movable scroll. A turnable ring is disposed between the pressure receiving member and the base plate. The ring has the first and second surfaces respectively facing the pressure receiving member and the base plate. The first surface of the ring has a plurality of first elements circumferentially spaces and provided at predetermined intervals. A plurality of first recesses are provided in the pressure receiving member, with the first elements fitted into the first recesses respectively. The second surface of the ring has a plurality of second elements circumferentially spaced and provided at predetermined intervals. A plurality of second recesses are provided in the base plate, with the second elements fitted into the second recesses respectively. When the movable scroll revolves, the first and second elements move within the first and second recesses to prevent rotation of the movable scroll and the ring. To transmit the compression reaction force of the gas acting on the movable scroll to the pressure receiving member, the first and second surfaces of the ring are provided with a plurality of projections protruding toward the pressure receiving member and the base plate and having substantially spherical engagement surfaces to engage therewith.