PURPOSE: To let a truck steer automatically as well as to make its smooth driving attainable, by coupling each pair of front and rear wheels intelockingly with each of front and rear traction levers via a steering knuckle and an interlocking link, while installing a device which lockes each of these front and rear traction levers to each straight drive attitude.

CONSTITUTION: A truck body 1 is provided with each of a symmetrical pair of wheels 2 and 8 and a pair of symmetrically rockable traction levers 5 and 11 in front and in the rear. In this case, a pair of front wheels 2 are interlockingly coupled with the front traction lever 5 via a steering knuckle 4 and an interlocking link 7 at both sides. Likewise, a pair of rear wheels 8 is also interlockingly coupled with the rear traction lever 11 via a steering knuckle 10 and interlocking link 23 at both sides. And, there are provided with traction lever locking devices 14 and 15 having a lock pin 17 liftably supported by a guide being secured tight to the front and rear of the truck body 1. With this constitution, these traction levers 5 and 11 at the opposite side to a traction direction is surely locked in advance so that the truck body 1 is travelable in the traction direction.