An inner pressure of an actuator is measured by a pressure measuring unit, and an amount of displacement of a movable mechanism is measured so that a position error compensation unit to which a desired value for the displacement and the measured value are inputted is allowed to compensate for a position error, and a desired value for a pressure difference of actuators that are competitively driven from the desired value is calculated by a desired pressure difference calculation unit, and an adjusted correcting value of the desired value for the pressure difference, obtained from the desired value of displacement and the measured value, is adjustably outputted from an adjustable desired inner-state correction unit, and thus, the outputs of these unit are inputted to a pressure difference error compensation unit so that a pressure difference error is compensated therewith.