PURPOSE: To reduce noises produced during operation of a compressor and to raise the efficiency of operation, by reducing the volume of a space filled with gas by charging many balls in the space formed between a compressor section and an enclosed case.

CONSTITUTION: When a rotor 3b is set into rotation by passing current to a motor section 3, a rotary piston 8 is turned by a crank shaft 6 and coolant gas drawn into a compression chamber 11 from an intake pipe 19 is compressed along with rotation of the piston 8. The compressed gas is once discharged into a space 17a in an enclosed case 2 via a discharge valve 9c and then carried to a refrigerating cycle via an inner discharge pipe 18a. Here, many balls 17 made of a material having a lower specific weight than oil are charged in the space 17a formed in the enclosed case 2 on the side of a compressor section, and coolant gas discharged from the discharge valve 9c via a discharge hole 9b is carried to the inner discharge pipe 18a through the gaps formed between the balls 17. With such an arrangement, it is enabled to reduce the volume of the space filled with discharged gas and to attain the required objects.