An internal pressure of a hydropneumatic drive actuator is measured by a pressure measurement device, a displacement amount of a movable mechanism is measured, a desired value and a measurement value of the displacement are inputted so that a position error is compensated by a position error compensation device, a desired value of a pressure difference of the actuator to which antagonistic driving is performed by the desired value is calculated by a desired pressure difference calculation device, outputs from the position error compensation device, the desired pressure difference calculation device, and the pressure measurement device are inputted, and a pressure difference error is compensated by pressure difference error compensation device.