PURPOSE: To optimize the distribution of load on the front and the rear wheels and to correct the position of gravity center by shifting a weight in machine direction with an actuator corresponding to the variation of the load distribution between the front wheel and the rear wheel.

CONSTITUTION: A lift arm angle sensor 41, a liquid level sensor 42 and a position lever 15 are connected to a controller and a servo-motor is controlled according to the variation of the load distribution ratio between the front wheels 2, 2 and the rear wheels 3, 3. The servo-motor drives a pump and transfers liquid between tanks 20, 21 to adjust the position of the gravity center.