A cylindrical portion 10 is not quenched, and its hardness of a cylindrical portion 10 is set at Hv200 to 300. An average cross sectional area of the crystal particle in this portion is set to be within 0.3 mm.sup.2. Accordingly, when a caulking portion is formed by expanding the cylindrical portion 10b to an inner ring 3 to a hub 2b made of carbon steel, cracks or the like are not formed in the resultant caulking portion.