To provide an apparatus and method for attaching a wheel bearing device which effectively suppress the expansion of a ring in caulking and prevent an outer peripheral spline of the ring from being deformed.

In the apparatus for attaching the wheel bearing device, the ring 21, on which the outer peripheral spline 21b is formed, is fitted onto the end of a small diameter step 4b of a hub wheel 4, and the ring 21 and an inner race 7 are fixed onto the small diameter part 4b so as to keep the rings from slipping therefrom by means of caulked part 11 formed by plastically deforming the end of the small diameter part 4b in an outward radial direction. The apparatus includes a restraining ring 28 which prevents diameter expansion of the ring 21 by being externally fitted onto the outer peripheral spline part 21b of the ring 21 when the caulked part 11 is worked. A spline 30, which has the same specifications as the outer peripheral spline part 21b of the ring body 21 and is engaged with the outer peripheral spline part 21b of the ring body 21, is formed on the inner periphery of the restraining ring 28, and the inner periphery of the spline 30 is gradually tapered toward the inner side thereof.