To provide an automatic flight control system for an airplane capable of greatly simplifying the modifying operation when the system is to be installed in the airplane.

The automatic flight control system 1 is equipped with a navigation device 2 designed to be mounted in an airplane for guiding it following the specified flying route, actuators 3a-3d for driving the control surface of the airplane, and a flight computer 4 to control the actuators 3a-3d. The arrangement further includes a casing 10 to accommodate the navigation device 2, the actuators 3a-3d, and the flight computer 4, a fixing means to fix the casing 10 to the pilot seat S of the airplane, and additional rods 30a-30d for transmitting the driving forces of the actuators 3a-3d to the control surface.