PURPOSE: To keep the position of an airframe by providing at the nose of the aircraft a movable control board which is longitudinally movable and which when in a forwardly projected position generates pitching moments in a direction for lifting the nose.

CONSTITUTION: During normal flight, an aircraft flies with a movable control board 2 put in a nose part 1 by an actuator 4. During a takeoff and landing at which pitching moments are generated in a direction for lowering the nose, the movable control board 2 is moved onto a rail 3 by the actuator 4 and projected diagonally upwards. At this projected position the movable control board 2 generates vortices 5 even with a small elevation angle of the takeoff or landing, thereby generating pitching moments in a direction for lifting the nose, Therefore, the pitching moments which are generated in a nose-lowering direction as when landing gear and flaps are lowered can be canceled out.