To provide a power transmission excellent in durability and productivity.

A pulley 1 with engaging teeth 1f formed thereon is rotatably supported by a cylindrical projecting part A of a compressor. A hub assembly 3 is fitted to a rotary shaft B of the compressor. In the hub assembly 3, a connection plate 7 is supported by the flange part 4b of a hub 4 through a leaf spring member 6. Engaging teeth are formed in the connection plate 7, and engaged with engaging teeth 1f of the pulley 1. When the rotary shaft B is in a locked condition, the engaging teeth 1f ride over the engaging teeth against the elastic restoration force of the leaf spring member 6. The leaf spring member 6 is inverted, and the engaging teeth are disengaged from the engaging teeth 1f.