To prevent an invasion of water into a bearing.

An oil-removing aperture 50 of a backing plate 40 is formed on a projecting portion 40A forwardly deviated from the lowermost point 26B of a flange portion 26A in which water drops W are accumulated. As a result, since water drops accumulated in the lowermost point 26B of the flange portion 26A of a housing end 26 rearwardly flows and is dropped by a wind pressure at the time of a vehicle traveling, it can be prevented that the water drops are invaded from the oil-removing aperture 50 into a space 44 even if the inside of the space 44 formed at an inner side portion of a bearing retainer 42 becomes a negative pressure by a rotation of a rear axle shaft 10.