A protruding section facing a drive pinion shaft is integrally provided on (or provided as a separate component) a tubular spacer interposed between an inner race of a pilot bearing and an inner race of a tapered roller bearing at an inner section opposite to the drive pinion shaft. In one embodiment, a monolithic protruding section is curved so as to be convex along the overall central axial direction of the spacer, and is arch shaped in cross section. The protruding section protrudes towards the drive pinion shaft along the overall inner peripheral direction of the spacer, and the inner surface of the protruding section comes into contact with or close to the outer surface of the drive pinion shaft. Additional positions include one or a plurality of O-rings interposed between the drive pinion shaft and the inner surface of the tubular spacer.