In a rotor member fixed by press-fitting to a rotary shaft part of an electric motor, the inner circumferential face of a sleeve part has an inner circumferential tapered face in which the inside diameter of the sleeve part continuously increases at a fixed ratio in a direction from a first end towards a second end. In addition, an outer circumferential face of the sleeve part has an outer circumferential tapered face in which the outside diameter of the sleeve part continuously decreases at a fixed ratio in a direction from the first end towards the second end in an axial-direction segment of the sleeve part in which at least the inner circumferential tapered face is present.