PURPOSE: To allow the driving wheels of an automated guided vehicle to be grounded in a desired direction such as a rectilinear direction at the time of grounding the driving wheels again after separating them from the road surface, thereby preventing the automated guided vehicle from traveling against an operator's will.

CONSTITUTION: A cam ring 148 different in outer diameter 180° by 180° is fitted to the outer peripheral part of a cylinder member 116, and a limit switch 150 is disposed correspondingly. Which lateral direction tires 104 are turned is discriminated by the contact of the limit switch 150. According to the discriminated result, the tires 104 are steered in the reverse direction and stopped when the contact of the limit switch 150 is switched. The tires 104 are thereby stopped in the state of facing straight. The tires 104 can be also held in the rectilinear state with relatively light magnetic force by magnetic bodies 162, 164.