PURPOSE: To improve the extent of ameliorations in both lift and pitching moment characteristics, etc., by installing an actuator and a power plant moving a fence, and making this fence operate so as to be projected over a wing surface at time of a large elevation angle.

CONSTITUTION: A fence 15 is installed in space between clamping parts 17, and it is made free of movements in an interval between these clamping parts 17 by dint of each power of an electric motor 19 and an actuator 18. A pilot operates a switch 22, operating a hydraulic power unit or the motor 19 and the actuator 18, and at time of a large elevation angle, the fence 15 is projected over the outside of a main wing 2, through which each relationship between lift and elevation angle, pitching moment and elevation angle, and between rolling moment by an apron 6 and the elevation angle is improved respectively. On the other hand, when a function of this fence 15 becomes unnecessary, it is retracted to be yet more downward than height of the clamping parts 17, whereby any resistance by air is reduced, thus deterioration in the cruising performance of aircraft is prevented from occurring.