PURPOSE: To provide an apparatus which enables the body to be invariably maintained horizontal by means of a hydraulic cylinder adapted to vertically move both front wheels provided on a king pin section thereof, communicated with an oil passage interlaid with an opening/closing valve for sensing a horizontal inclination of the cylinder.

CONSTITUTION: It is assumed that a vehicle is inclined by a higher left side while travelling on an uneven ground. Among a pair of hydraulic cylinders 6 and 7 connecting a piston rod to a shaft of wheels 3 and 4, a piston 11 in a right hydraulic cylinder further lowers, so that the hydraulic force in an upper chamber 9 decreases. Consequently, oil flows to the upper chamber 9 on the ritht side in the direction of the arrow C passing through an oil passage 18 from an upper chamber 9 in the left hydraulic cylinder 7. In this manner, both the wheels 3 and 4 move vertically in the directions of A and B to be adjusted so that the body is balanced properly. In this case, when the body is inclined a great deal, a pendulum 20 with a weight 19 oscillates to close an opening/closing valve 17 of the oil passage 18