A hub for use in a power transmission apparatus comprises cylindrical portion 81 and outer ring 83 including a plurality of tongue-like reinforcing portions 83c each protruded radially inward from the peripheral end of the corresponding one of the plurality of protrusions 83b. When the distance from point C where the rear-side end surface of the cylindrical portion 81 and hub-side engaging portion 85 are connected with each other, to rear-side end surface D of reinforcing portions 83c is given a, and the distance from rear-side end surface D of reinforcing portions 83c to radially innermost front-side portion E is given b, distance b is less than one half of distance a.