PURPOSE: To delay the stalling of a main wing in case of the large angle of incidence and reduce the flight resistance in the navigation state with the supersonic speed and the transonic speed, by controlling the intensity of a swirl generated from a strake by allowing the planary shape of the strake to be changed according to the flight state.

CONSTITUTION: A strake 1 is constituted so as to be rotatable within a nearly a plane around the revolution center of a wing root, over the range from the front edge of a main wing 3 to an airframe 4, and the shape and area can be varied from the planary shape in the case of a large angle of incidence to the planary shape in navigation. A gap cover 5 is installed in the gap generated because of the separation of the rear end of the strake 1 from the front edge of the main wing 3 during the turn of the strake 1 from case of the large angle of incidence to navigation. Accordingly, during flight, the area is increased by turning the strake 1 in case of the large angle of incidence, and a strong swirl is generated, and the stalling of the main wing 3 is prevented, and the large angle-of-incidence flight is enabled, while the area of the strake 1 is reduced during navigation, and the flight resistance can be reduced.