PURPOSE: To reduce a turning radius along with the reduction of side slip by controlling a control valve in response to signals sent from a car speed sensor and a steering amount sensor.

CONSTITUTION: A signal from a car speed sensor 41 is always inputted into a control unit 48 when a truck 50 runs. When forward car wheel axles 14, 15 are steered by the operation of a steering wheel 19 at low speed travelling, a steering sensor 42 detects the rotational speed, direction of rotation, and turning angle of a steering shaft 20, sending an output signal to its control unit 48. Said control unit 48 controls a solenoid valve 45 based on a previously stored turning pattern in response to said output signal, allowing an actuator 36 to be driven and the rear car wheel axles 29, 30 of a rear steering 26 to be steered.