To provide a fluid machine working as a rotary means with simple configuration which is difficult to damage and is superior in utility.

The machine accommodates a rotor in its entirety 11 of a main rotor 10, a protuberance 13 protruded from the rotor in its entirety 11, and a rotor in its entirety 21 of an auxiliary rotor 20 which contacts contacted outer peripheral surface 21a on outer peripheral surface of the rotor in its entirety 11 and has recessed concave outer peripheral surface 21b of the protuberance 13 of the main rotor 10. The elements described above are housed into a rotor chamber in such condition that tip of the protuberance 13 of the main rotor 10 is brought into slide contact with the inner peripheral wall surface 30b of a first chamber, and the contacted outer peripheral surface 21a of the auxiliary rotor 20 is brought into slide contact with inner peripheral wall surface 30c of the second chamber. The machine drives the main rotor 10 provided with the protuberance 13 by flowing fluid into the rotor chamber 30. In addition, the rotor shaft of the main rotor 10 serving as an input driving shaft renders intake and exhaust.