Crowning is applied to a side surface of an inner ring which abuts against a side surface of a drive shaft in a radial direction. With this construction, when the two side surfaces abut against each other by a pressing operation of a threadedly-engaged nut at the time of connecting the drive shaft and an inner shaft, a contact pressure distribution of abutting surfaces is made generally uniform, thereby suppressing the occurrence of an edge load. By thus preventing a contact pressure from increasing at part of the abutting surfaces, energy released by a stick-slip phenomenon is reduced, and a sound pressure level of an abnormal sound generated at this time is reduced.