Rotation preventing mechanism using thrust ball bearing and scroll type compressor using the same

A scroll type compressor including a pair of swirl members disposed in a casing in confrontation with each other and discharging drawn refrigerant while compressing it by executing a relative turning motion by one of the pair of swirl members while preventing the rotation of the one swirl member with respect to the other swirl member by a rotation preventing mechanism substantially composed of a thrust ball bearing, the thrust ball bearing including a first annular race section, a second annular race section disposed in confrontation with the first annular race section, thrust balls interposed between the first and second annular race sections, the first and the second annular race sections having ball accommodating grooves formed to each of the confronting surfaces of the first and second race sections in which the thrust balls are accommodated so as to turn in a direction along the confronting surfaces, wherein each of the ball accommodating grooves of at least one of the first and second annular race sections has a central portion and a groove bottom portion around the central portion, and the ball accommodating groove has a shape satisfying the relationship of an inequality RB.ltoreq.Rin<Rout, when the radius of curvature of the thrust ball, the radius of curvature of the cross section of each of the ball accommodating grooves inside the groove bottom portion, and the radius of curvature thereof outside the groove bottom portion are represented by RB, Rin, and Rout, respectively.