A rolling bearing is provided on an outer peripheral surface of a hub spindle of a hub wheel on which a wheel is mounted. Opposite side face splines, which, by meshing with each other, couple the hub spindle and an outer ring of a constant velocity joint torque-transmittably, are respectively formed on an end face of the hub spindle and on an end face of the outer ring of the constant velocity joint which is abutted against this end face. A tubular seal member for covering outer peripheries of the opposite side face splines is disposed so as to straddle an inner ring of the rolling bearing and the outer ring of the constant velocity joint, while maintaining a sealing state.