Abstract: A roller 58 is rotatably held by an end portion of an eccentric support roller shaft 50 so that the roller 58 contacts with an inner periphery circular side surface of a rotor 40. Accordingly, a rotational resistance while the rotor 40 is eccentrically rotated can be decreased in comparison with a configuration in which an internal gear formed in an inner periphery of a rotor and an external gear formed in an eccentric shaft interlock each other. Thus, the rotating shaft 52 can be efficiently driven to rotate when a pressure difference is small and energy for rotating the roller 58 is small.