To heighten the engine efficiency and establish a constant quantity of oil flow through a smooth on-off operation of oil feeding by pressure.

A flange-equipped pressure piece 16 in cylindrical shape is interposed between an inner rotor 9 and crank shaft 3 and coupled with a crank shaft 3 movably in the axial direction, and a clutch plate 19 is interposed between a disc surface of the inner rotor 9 and the flange 16b, and an initially coned disc spring 18 is installed on the back of the flange 16b mating with a clutch plate 19, and the end face 16a of the pressure piece 16 is positioned confronting a pressure chamber 17. The clutch plate 19 starts sliding with a certain pressure of oil discharged to cause the revolving speed of the inner rotor 9 to lower below the crank rotation speed, which sinks the discharge pressure, so that it is practicable to adjust the oil supply quantity. The sink of the discharge pressure causes engagement of the clutch plate 19, on the way whereof an intermediate condition of on-off operation is generated, which allows keeping constant the oil pressure with a mild transition and enhancing the engine efficiency.