To improve the durability of tapered roller bearing and a ball bearing to support a pinion shall while securing the lubricity of the bearings.

An outer circumferential edge of a second seal ring 26 is locked to an inner circumferential surface of a rear end part of an outer ring 6. An inner circumferential edge of a rubber seal lip to constitute the second seal ring 26 is brought into slidable contact with an outer circumferential surface of a pinion shaft 1 over the whole circumference. The lubricating oil stored in a casing 3 passes a slidably contact part of the inner circumferential edge of the seal lip with the outer circumferential surface of the pinion shaft 1, and enters a tapered roller bearing 12. Foreign matters such as abrasion powder mixed in the lubricating oil can not pass the slidably contact part, and are retained within the casing 3.