An opening end of an inboard section includes: an end surface composed of a plane positioned farthest from the center of a differential device in the axial direction and perpendicular to the axial direction; a ledge positioned adjacent to the end surface in the circumferential direction of the opening end and closer to the center than the end surface in the axial direction; and a tapered section in a slope shape formed continuing to the inner diameter side of the ledge at the opening end, slanting toward the inner diameter side of the opening end and approaching the center. Lubricating oil supplied to the opening end of the inboard section flows to the tapered section via the ledge and flows from the tapered section into a spiral groove formed on an inner periphery of the inboard section.