A hub unit is fixed to a body's side in such a state that a lubricating ring member is held between a hub receiving surface which constitutes a step portion of a large-diameter portion and a vehicle inner side end face of an inner ring with at least either of an abutment surface of the lubricating ring member with the hub receiving surface and an abutment surface thereof with the vehicle inner end face of the inner ring made to constitute a lubricant holding surface which holds a lubricant, whereby the hub receiving surface and the vehicle inner side end face of the inner ring are made to easily slip relative to each other, thereby making it possible to prevent the generation of an abnormal noise between contact surfaces of the inner ring and the hub receiving surface of the axle.