PURPOSE: To shorten time required for rim fastening work by unitizing members for alignment to prevent them from dispersing.

CONSTITUTION: The rim of a wheel is fastened to a flange member 4 fixed to the shaft 1 with a fastening means 6. The shaft 1 has a conical peripheral surface 8 having a diameter extending gradually in the direction of fastening, and a diameter extending member 9 freely extensible in the radial direction having a conical inner circumferential surface 10 which touches and slides on this conical peripheral surface 8 and a cylindrical peripheral surface 12 which joins to the center hole of the rim 5, is provided. The diameter extending member 9 has a cylindrical ring 14 having a flange 15 and a flangelike touching and supporting means 17, and an angle ring 18 which covers the touching and supporting means 17 from its rear side over to its radial-direction outside is provided in such a way as to be abel to move sliding freely in the axial direction of the diameter extending member 9. The cylindrical part 19 of the angle ring 18 touches the rear of the rim 5, and a spring 21 is fitted maintaining its initially energized state between the flange 15 and the disklike part 20 of the angle ring 18.