A control system of an aircraft includes a computer that controls flight based on either a flight control law that controls flight by controlling the deflection angles of control surfaces or a control surface/thrust integrated flight control law that controls flight by controlling the deflection angles of the control surfaces and engine thrust, and a control surface failure/damage detection device. If malfunctioning of the control surface(s) is detected, the deflection angles and the rates of change of the deflection angles of the control surfaces are calculated based on the detection result, and the necessity of switching from the flight control law to the control surface/thrust integrated flight control law is judged by judging whether or not the calculated deflection angles or rates of change of the deflection angles exceed an acceptable range of change.