PURPOSE: To determine the optimum driving amount of an actuator corresponding to the situation by processing the difference and the variation of the difference between the theoretical rotational angle of a lift arm from the real angle based on fuzzy inference.

CONSTITUTION: The moving amount of a lift arm is set by a position lever 14 and the real moving amount is detected by a lift arm angle sensor 16. The preset value is compared with the detected value by a difference calculation means and the variation of the difference is calculated by a variation calculation means. The difference and its variation are processed by a driving amount determination means based on fuzzy inference to determine the subsequent driving amount of a hydraulic cylinder 10.