PURPOSE: To provide possibility of air supply to a rotor with different pressure by connecting a plurality of air circuits independently by the use of seal due to a minor air gap at the rotor and a stationary part.

CONSTITUTION: Ports a-d bored in a stationary pipe 2 are leading to respective ports A-D through grooves cut in a rotor 1 and holes bored in the grooves. Therein the seal of the ports between is made with a minor gap to be formed between the periphery of the rotor 1 and the internal surface of the stationary pipe 2. Other ports (e), (f) are furnished as exhausting port in order to nullify influence of oil etc. of bearings 6, 7. Thus air supply to the rotor is made practicable with a plurality of independent circuits, and it is also made practicable to make air supply with different pressures.