A power transmission apparatus comprising a pulley 1 and a hub 2 is disclosed. The hub 2 includes an inner hub 21 fixed on a rotary shaft 4 and an elastic member 23 coupled over a joint length L to the outer periphery of the inner hub 21. Elastic member 23 includes a hub-side engaging portion having a series of protrusions arranged in a ring and a cylindrical portion connecting the hub-side engaging portion and the inner hub. Pulley 1 has a pulley-side engaging portion having a series of depressions fitted on the hub-side engaging portion. The engagement between hub-side engaging portion 235 and pulley-side engaging portion 14 forms a torque transmission structure of hub 2 and pulley 1. An axial length TL of a torque transmission surface TS formed by hub-side engaging portion 235 and pulley-side engaging portion 14 in contact with each other is larger than joint length L between the cylindrical portion and inner hub 21. Axial length TL, when projected in the radial direction, is partially overlapped with joint length L.