To provide an expansion aerodynamic surface for forming a lifting surface by expanding a plate-like small wing from both gunwales of the body of an airplane and using this also as a steering wing or a brake.

An expansion aerodynamic surface includes pivot shafts 15 erected in recesses 14 plotted in left and right gunwale sides so as to be obliquely moved freely in pitch directions and a plurality of plate-like small wings 20 having base end parts pivotally attached to the pivot shafts 15, housed in the recesses 14 being laminated in the directions of the pivot shafts 15 and expanded like fans around the pivot shafts 15 to form lifting surfaces. Thus, the expansion aerodynamic surface is used as a high lifting device and, by changing the areas of the lifting surface surfaces of the left and right gunwale sides or incidence angles, this is used as a steering wing for producing roll motion and further, by making the lifting force surfaces to be large pitch angles by the turn of the pivot shafts, this is used as a speed brake.