allows the movable scroll to revolve and it is arranged between the movable scroll and a front housing in fig7 a spiral body 20b of the movable scroll 20 engages with a spiral body 16b of a fixed scroll an end plate 20a of the movable scroll 20 and a thick disk shaped bush 21 are arranged concentric with each other and the bush 21 rotatably fits into a boss 20c of the movable scroll 20 through a needle bearing 22 to the end plate 20a of the movable scroll 20 on the side of the front housing 10b there is fixed a movable race 25 shown in fig8 a and to the front housing 10b on the side of the movable scroll 20 there is fixed a fixed race 24 shown in fig8 c further between six ball rolling grooves 25c of the movable race 25 and six ball rolling grooves 24c of the fixed race 24 there are interposed balls 26 respectively an o ring 27 is disposed between the front housing 10b and a rear housing in fig8 a on the circumference of the ring shaped movable race 25 having a radius r there are provided the six annular ball rolling grooves 25c at equal intervals at the center of each of the ball rolling grooves 25c there is formed a projection 25e about which the ball rolls similarly in fig8 c.