Either an inner ring or an outer ring is formed to protrude in the direction of the rotation axis more than the other of outer ring or inner ring. For example, the bearing 12 is supported by the bearing housing 11a on the outer peripheral face 12b of the outer ring, and rotatably supports the hub 31a on the inner peripheral face 12a of the inner ring. In this bearing 12, the inner ring is formed to be longer and protrude further than the outer ring in the direction of the rotation axis, and an engagement/support face 12c for enagageably supporting the drive sprocket 92 is formed on the outer periphery of the inner ring formed to protrude as described above. The drive sprocket 92 is able to secure the coaxiality thereof by the engagement with the engagement/support face 12c, and receive the transmittance of rotating torque by engaging with the hub-side spline 31c on the spline 92c.