To improve the compression efficiency by bringing end faces of inner and outer rotors into slidable contact with a board surface of a discharge hole board in a liquid-tight manner by the axial force due to the discharge pressure to be applied to the discharge hole board interposed between the inner and outer rotors and in inner surface of a discharge port bracket to reduce the leakage of the fluid from the end face part.

A fluid flowing into a variable space by the rotation of an inner rotor 2 and an outer rotor 1 is compressed as the displacement of the variable space is reduced, and fed through a discharge port 7 from discharge holes. When the pressure in a discharge chamber 11 is increased, a discharge hole board 4 is pressed toward the suction side, and the board surface 4a is abutted on an end face 30 on the discharge side of rotors 2, 1. The rotors 2, 1 are also slightly moved by the axial force from the discharge hole board 4 until an end face 31 on the suction side is abutted on an inner surface 8a of a suction port bracket 8, and the rotors 2, 1 are rotated while the water-tight condition is kept at the slidably contacted part of the end faces 31, 30 with the inner surface 8a of the suction port bracket 8 and the board surface 4a of the discharge hole board 4.