To enhance the whole rigidity of a fastening part by stabilizing tightening moment of a hub bolt.

A washer 30 is arranged on an outer peripheral part of a taper part 28 at the hub nut side in the hub nut 24 with a gap S1 in an axial direction of the hub nut 24 and a gap S2 in a radial direction of the hub nut 24 against the hub nut 24. The washer 30 is movable in the axial direction and radial direction of the hub nut 24 by a predetermined distance. Since a dishing part 32A and a recessed part 32B are formed at a small diameter part side of the washer 30 and a recessed part 28A is formed at a small diameter part side of the taper part 28 at the hub nut side, the washer 30 contacts a hole side taper part 26 only by a contact surface 32C at a large diameter side, and contacts the taper part 28 at the hub nut side only by a contact surface 34A at the large diameter side.