A control input for operating an actual vehicle actuator and a control input for operating a vehicle model are determined by an FB distribution law based on a state amount error which is a difference between a reference state amount determined by a vehicle model and an actual state amount of an actual vehicle such that the state amount error is approximated to zero. An actuator device of the actual vehicle and the model vehicle, respectively, are then operated based on the control inputs. The FB distribution law estimates an external force acting on the actual vehicle due to a control input for operating an actual vehicle actuator, and determines a control input for operating the vehicle model on the basis of the estimated value and a basic value of a control input for operating the vehicle model for approximating the state amount error to zero.