To reduce an inner ring difference and improve natural turning performance having a sense of unity and stability by towing a front steering shaft type trailer by a tractor, detecting the forward and backward traveling direction of the tractor to switch a transmission system of a transmitting member, and converting the steering direction of the trailer to the steering direction of the tractor.

A lunette eye 12 of a towing lever 3 is connected to a pintle hook 4 of a tractor through a joint and a bracket 11 which are projected from a trailer to move vertically and laterally. A intersecting angle of the towing lever 3 and the trailer is detected by a steering amount detecting arm 13, and an amount of this motion is transmitted through a link lever 14, a forward-reverse steering direction switching mechanism 9, and the respective transmission means 16-20 following a connecting rod 15 to a steering wheel 6 to be steered. That is, the steering direction switching mechanism 9 is operated in the reverse direction by an electromagnetic solenoid 8 so that at the time of forward movement, the steering wheel 6 of the trailer is steered according to the steering direction of the tractor, and at the time of reverse movement, the steering wheel 6 of the trailer is steered in the opposite direction to the steering direction of the tractor.