PURPOSE: To improve the tolerance of the material used in a compressor of which compressing members driven eccentrically are made of a magnesium alloy and points thereof are confined by circumferentially extending walls of conveying spaces by making the circumferentially extending spiral walls forming the conveying spaces with a magnesium alloy.

CONSTITUTION: A rotor 1 of the described compressor comprises two spiral- shaped compressing members (strips) 3a, 3b which are offset by 180°, attached to both sides of a disc 2 forming a part of a main shaft 24. The disc 2 is retained on an eccentric disc 23 via a boss 4 and a roller bearing 22. Elements 2, 3a, 3b, 4 are made as one piece of a magnesium alloy. The rotor 1 is accommodated in a housing having two conveying spaces 11a, 11b which are offset by 180°. In such a compressor, housing halves 7a, 7b forming the housing and webs 45a, 45b, 46a, 46b forming the conveying spaces 11a, 11b are made as one piece of the magnesium alloy.