To provide a rotary piston machine achieved in high efficiency and a low fuel consumption ratio, and suppressed in the generation of pollutants.

A rotor has a rotor axial line A and a circumferential surface, each vane is radially extended from an inner surface of a housing plate 5e toward the rotor axial line, and an actuation chamber is defined by the inner circumferential surface of a housing, the circumferential surface of the rotor, and a side surface of at least one vane 1a. Each vane is connected to one end of a control arm 7 in the form of a joint in such a way as to rotate around the axial line. The other end of the control arm is rotatably supported by an axial center shaft 8 that is fixed. The shaft has a center axial line B that coincides with an axial line extended along the center of a hollow part of the housing. The center axial line is extended at an interval from the rotor axis in parallel to it. The rotor properly constitutes a unit for power to be taken out or inputted.