To provide a feedback control system suitable for estimating and compensating nonlinear system disturbance by making the system include a disturbance estimation and control device and adding controller output signals generated by the device and output compensation signals, and generating compensated plate target value signals for driving a plant.

The controller output signals 46 directly drive an actuator model 40 and output signals 31 are generated by a scaling element 30a. The output signals 31 are connected to the plant 55 as main control output signals for the plant. A disturbance estimation and control device 60 estimates the disturbance acting on the system by using deviation signals on a line 42 and generates force required for cancel the disturbance. The deviation signals are obtained by comparing actuator position signals on the line 56 with a model actuator position state on the line 43. Opposite force generated by the disturbance estimation and control device 60 is added to compensator signals 31 and control signals 32 are generated. The control signals 32 drive an actuator (plant 55).