PURPOSE: To improve the sealability of a threaded-rotor compressor by reducing the load of spigots driven in the compressor, imparting high rigidity to each rotor as a whole, and reducing a sealing gap between the end face of each rotor and a casing portion to a minimum.

CONSTITUTION: This threaded-rotor compressor, having externally and internally threaded rotors which mesh with each other, has a suction side bearing casing 3 and a delivery side bearing casing 15 which have spigots 14 protruding into bores in the rotors 12, 12a. The rotors 12, 12a are supported by radial bearings 6, 22 and axial bearings 9, 12 on the suction side. Radial bearings 16, 17 are used for supporting the rotors 12, 12a on the delivery side. A torsion shaft 4 for the joint portion 1 of a compressor drive is guided through a bore in the suction side bearing casing 3 and one of the four spigots 14, and a large diameter portion located on an inner end is connected to the recess of the bore in the rotor 12 in a form-locking manner.