A pump housing receives an outer rotor and an inner rotor. A joint member couples between a rotatable shaft and the inner rotor to transmit a rotational torque from the rotatable shaft to the inner rotor. A radial bearing is shaped into a cylindrical tubular form. A cylindrical inner peripheral surface of the radial bearing rotatably and slidably supports the rotatable shaft. A cylindrical outer peripheral surface of the radial bearing rotatably and slidably supports an inner peripheral surface of the inner rotor. A lubrication groove is formed in the cylindrical outer peripheral surface of the radial bearing and accumulates fluid, which is present in an inside of the pump housing.