PURPOSE: To improve productivity by mounting a compressor proper in a casing via a disc plate having the external side thereof approximately equal to the casing in diameter and fixed to the frame of the compressor proper.

CONSTITUTION: Casings 10 and 11 house a compressor proper comprising a shaft 13, a moving blade 15, a stationary blade 16, a stator 18 and a rotor 19. The outer diameter of a disc plate 20 is made approximately equal to that of a main casing 10 and the lower part of an upper casing 11 covers the external surface of the disc plate 20 and the main casing 10, thereby pressing the disc plate 20 sandwiched between the upper casing 11 and the main casing 10. As a result, the external surface of a frame does not need machining on a lathe and productivity can be enhanced.