To reduce bending moments transmitted to the rear edge of a wing even if a large force is applied to the front edge of the wing.

The upper and lower surface portions of a wing main body 2 are split from each other at a position halfway between a front edge and a rear edge, and these longitudinally split front and rear wing sections 11, 12 are rotatably connected together by hinge members 13. A deformation- restraint member 15 restraining the deformations of the surfaces of the hinge members 13 above and below the front and rear wing sections 11, 12 is placed within the wing main body 2, and the outer surface of the wing main body 2 is covered with a metallic thin plate 3.