To increase stability by providing an error exclusion section adding or averaging and feeding-back the differential pressure between hydraulic actuators with their output rods constrainedly operated together.

Stationary cylinders 6a, 6b generate the same differential pressure in opposite directions while a control object 7 is kept at a zero position due to the drift of the zero point of the electro-hydraulic servo valves of control system channels A, B in the stationary state. When a step input is applied, the cylinders 6a, 6b are changed to the ordinary state from the transition state and generate the same differential pressure in the opposite directions. When the differential pressures are added, only the difference between the differential pressures in the transition state is detected, static differential pressures due to errors of control systems are offset, and the differential pressures due to dynamic causes occupy the most part. When these signals are averaged, the output signal of an error exclusion section 14 is obtained. This signal component indicates the acceleration component of the control object 7, its feedback via a differentiating circuit 15 is equivalent to the acceleration feedback of the control object 7, and stability is compensated.