OIL PUMP

This oil pump is equipped with a rotatable inner rotor that includes a vane-housing unit housing multiple vanes so as to be capable of sliding in the radial direction, a rotatable annular outer rotor that includes multiple vane-connecting parts connecting the tip ends of the multiple vanes on the outside in the radial direction, first volume-changing parts, which are provided between the inner rotor and the outer rotor, and a first volume of which is changed in response to eccentricity of the inner rotor with respect to the outer rotor, thereby providing a pumping function, and second volume-changing parts, which are provided in the outer rotor, and a second volume of which is changed by a change in the distance between adjacent vane-connecting parts in the circumferential direction in response to eccentricity of the inner rotor with respect to the outer rotor, thereby providing a pumping function.