A clamping mechanism includes a pair of contact portions facing each other which is capable of directly contacting a tie rod hexagonal portion, and an open-close drive mechanism that causes the both contact portions to move away from and approach the tie rod hexagonal portion. By appropriately changing the distance between surfaces of the mutually facing pair of contact portions, the tie rod hexagonal portion will be securely clamped by the pair of contact portions, regardless of the size of the diameter of the tie rod. Then, the tie rod hexagonal portion is rotated to adjust the toe angle, by rotating the clamping mechanism via the rotation drive mechanism.