A power transmission apparatus includes a pulley 1 having a belt attached thereto to transmit the rotating drive force, a hub 2 which connects the pulley to a rotating shaft of a driven device, a bearing 7 which rotatably supports the pulley, and a sleeve ring 5 which is fitted and secured to the pulley and attaches the bearing to the pulley to prevent it relatively moving. The sleeve ring is provided, on its first end opposite to the driven device, with a bent portion 5b against which the bearing abuts to restrict further movement of the bearing. An annular retainer 6 is provided on the portion of the bearing adjacent to the drive device. The bearing is secured to the sleeve ring through the annular retainer by calking a second end 5a of the sleeve ring opposite to the first end. The sleeve ring is provided with a projection 5f which projects in the axial direction from the rear surface of the pulley and a casing 9 is provided with an annular groove 9c which at least partly receives therein the projection.