To provide a wheel bearing device assembled by using an automatic machine to reduce the number of assembling man-hours, and to provide its assembling method.

A method is provided for assembling the wheel bearing device which has a hardened irregular portion 15 formed on the inner diameter of a hub ring 1 and a cylindrical portion 10 bitten into the irregular portion 15 with its fitting portion 10b diameter-enlarged to plastically join the hub ring 1 integrally with an inner ring member 7. Herein, a tapered roller 6 is held by a cage 12 and fitted into an outside rolling surface 4a on the outer side of an outward member 4, and then a seal 14 is pressed into the outer end of the outward member 4, reversed and fitted into the hub ring 1 vertically arranged. While the tapered roller 6 in the state of being held on an inside rolling surface 7a by the cage 13 is fitted into the outside rolling surface 4a on the inner side, the cylindrical portion 10 is internally fitted into the hub ring 1. Finally, the seal 14 is mounted between the outward member 4 and the inner ring member 7 and an inward member 5 is plastically joined to the outward member 4 being in rotating motion relative to the hub ring 1 by caulking the enlarged diameter.