PURPOSE: To contrive reduction in steering resistance and enhancement in the degree of freedom of design by arranging a low ball joint, in a specific condition, on the inside of the inner circumferential periphery of the friction plate part in a brake disk so as to be approached to the central rotating surface of a wheel.

CONSTITUTION: A wheel hub 2 fixed to the outer end of a wheel driving shaft 1 by means of a nut 3 is fixed to a knuckle 9 via a ball bearing 10. And the ends of respective upper and lower control arms 14, 15 which have been journaled 13, 18 to a vehicle body B respectively are connected to a long arm 9a and a short arm 9b extending upward and downward from the knuckle 9 via upper and lower ball joints 16, 17 respectively. In this case, the lower ball joint 17 is arranged on the inside of the inner circumferential periphery of the friction plate part 6b in a brake disk 6. And a ball 25 is turned upward, and a ball stud 24 is fixed to the end of the lower control arm 15. Further, a socket 26 for housing the ball 25 is fixed to the short arm 9b.