PURPOSE: To prevent a deforming action for a hub assembly by adopting such a configuration that a bearing assembly is axially pulled by a coupling outer member applying to a front face of a bearing inner ring at an opposite face, wherein the opposite face is a cone in the coupling outer member, the front face of the cone engages with the bearing inner ring.

CONSTITUTION: A hub 11 is mounted on a threaded pin 18 of a coupling outer member 14. A bearing 22 is mounted on the hub 11. On the other hand, a second bearing inner ring 23 adjacent to the coupling is separately mounted on the hub 11. The bearing inner ring 23 is supported by a supporting surface 27 on the hub having a first front face 28. An opposite face 29a has an effect on a front face 30a lying the outside of the bearing inner ring 23. The opposite face 29a of the coupling outer member 14 is formed as a conical shape, and engages with the front face 30a of the complementary inner cone in an adjacent different bearing inner ring 23. As the result of the axial force due to the thread-nut device 18, 19, the opposite face 29a applies the axial force and the radial supporting force to the inner cone front face 30a to prevent its deformation.