To provide a spiraxial screw fluid machine for compressing suction fluid by a thread lead part inscribing with a casing when transferring the fluid from a suction side to a delivery discharge side within the casing, thereby obtaining a higher degree of vacuum and higher pressure and also a lowered final discharge temperature compared with a conventional arrangement.

This spiraxial screw fluid machine internally compresses at a plurality of stages by different thread leads from the suction to the rotor end fallowing rotation of the rotor in the area between the spiral surface of the rotor and a corresponding fluid space. Because of a compressing mechanism formed in the thread lead part, a high degree of vacuum and a high pressure can be secured, compared with a conventional spiraxial screw fluid machine. If the number of leads remains the same, the overall length of the rotor can be shortened compared conventional one.