PURPOSE: To prevent a thrust bearing from bearing a radial load by providing a spring of coil spring, belleville spring, etc. between the thrust bearing and a bearing retainer or in both sides of the thrust bearing, and fixing the thrust bearing by spring tension.

CONSTITUTION: A compressor provides male/female rotors 1, 2 meshed with each other, casing 3 for storing both the rotors, radial bearings 5a, 5b for supporting both the rotors, thrust bearings 6, 6a, 6b and bearing retainers 13a, 13b for fixing both the bearings. A coil spring 16 is provided between the thrust bearings 6, 6a, 6b and the bearing retainers 13a, 13b to fix the thrust bearings 6, 6a, 6b by spring tension. Further, the coil spring 16 is arranged concentrically in a plural quantity. In this way, the thrust bearings 6, 6a, 6b can be prevented from bearing a radial load, and a circular part clearance can be prevented from decreasing due to deformation of a thrust bearing outer ring.