A wheel bearing device is provided to prevent loosening of a hub ring and an outer joint ring that are fitted together. An irregular portion treated with hardening is formed on a fit face of the hub ring on an inside periphery of which the outer joint member is fitted. A low hardness portion of the outer joint member formed with hardness lower than that of the irregular portion is expanded in diameter to make it bite into the irregular portion. In this way the hub ring and the outer joint ring are unitized together.