To improve the working efficiency of polishing work by arranging slipping-out preventive members in tip parts of shafts, bringing the outside of buff wheels into contact with these slipping-out preventive members, and screw-fitting fastening nuts to the inside of the buff wheels in the shafts.

Slipping-out preventive pins 50 and 50 fitted to and installed on tip parts of small diameter parts 11 and 11 in shafts 10 and 10, prevent buff wheels 20 and 20 from falling off from the small diameter parts 11 and 11 of the shafts 10 and 10. In this condition, the buff wheels 20 and 20 are fastened and fixed by the slipping-out preventive pins 50 and 50 by screwing and moving fastening nuts 40 and 40 in the direction of the buff wheels 20 and 20. As a result, a projecting part is eliminated from outside surfaces of the buff wheels 20, and polishing work is more easily performed, and positioning of the buff wheels 20 to a vehicular wheel W is facilitated.