PURPOSE: To fix a steering device easily even at travel time when a connecting rod, hydraulic piping and the like are broken down by forming a recessed part or a projecting part on a steering board, and engaging a recessed and projecting piece moved by extension and contaction of a fluid pressure cylinder with the recessed part or the projecting part.

CONSTITUTION: A steering device of a trailer 10 is constituted by connecting rotary arms 24 on both sides of a wheel shaft 22 and a steering board 32 to each other by a connecting rod. Rotational displacement of a tractor 12 is transmitted to a cylinder 18 through a hydraulic pipe 16, and a rear steering board 20 is rotated, and this rotational displacement is transmitted to a front steering board 32 through a connecting rod 32. A recessed part 42 is formed on the front steering board 32, and when a projecting piece 48 rotated by extension and contraction of a fluid pressure cylinder 44 with a shaft 46 as its center is engaged with the recessed part 42, rotation of the front steering board 32 is stopped. Thereby, since a part of the other steering device connected by a link mechanism is also fixed, when failure is caused in the connecting rod and the like, there is no need to fix the steering board by a pin by jacking up the wheel shaft, so that the steering device can be fixed easily at travel time.