PURPOSE: To enhance the efficiency and to lower the temperature rise in a compressor which compresses the gas like the air by giving free rotation to a part of or the entire of the flow passage of a stator.

CONSTITUTION: When a moving vane 1 of a centrifugal compressor 8 rotates on account of rotation of a shaft 6, the gas, which comes in through a suction port 5, is accelerated to comes back again to a moving vane 1' via both a stationary guide tube 2 and a curved part 3. A freely movable, rotating guide- tube 4 is arranged to the curved part of a stationary guide tube 2' via a sliding bearing 64, and the relative speed of the gas within the freely movable, rotating guide-tube 4 is slowed down. In addition, the amount of generation of heat in this part is also lessened. By suppressing the temperature-rise, it becomes possible to compress the gas with efficiency that is almost equal to the efficiency in an isothermal change.