said movable scroll for compressing gas in the compression chamber a first ring orbits together with the movable scroll between the movable scroll and the housing for receiving compressive reaction force acting on the movable scroll a second ring which is secured to the housing receives the compressive reaction force received by and acting on the ring application_number US 22706194 A description one embodiment of the present invention will now be described specifically with reference to fig1 through 4 as shown in fig1 an aluminum fixed scroll 1 has a casing 2 an end plate 3 and a spiral element 4 a discharge port 5 is formed in the end plate 3 and is positioned in the spiral center of the spiral element 4 a reed valve 6 is provided to open and close the discharge port 5 a retainer 7 serves to prevent the reed valve 6 from being open too much an outer wall 8 is fixed to the outer surface of the end plate 3 with a discharge chamber 9 defined between the end plate 3 and the outer wall 8 the discharge chamber 9 is connected to an external cooling circuit via a pipe not shown an aluminum housing.