A high-lift system on the airfoil of an aircraft, comprising a main wing (H) which has a curved main wing nose (N) and comprising a leading-edge flap (V) is disposed retractably on the main wing (H) by means of an arrangement of several levers (a, b, c) so that said leading-edge flap can be moved from a retracted position (I) whilst increasing the expansion of the airfoil profile in the chord direction and whilst increasing its curvature and whilst exposing a gap (g) which guides energetic air from the underside of the leading-edge flap (V) to the upper side of the main wing (H), as far as a fully extended position (III). According to the invention, the lever arrangement (a, b, c) is configured in the form of a four-bar mechanism and comprises a first lever (a) and a second lever (b), of which the first lever (a) is connected at one end to a first point (A) on the main wing (H) in an articulated manner and the second lever (B) is connected at one end to a second point (B) at a distance therefrom on the main wing (H) in an articulated manner, and which are each connected at the respectively other end in an articulated manner to the opposite ends of a third lever (c) which is part of the leading-edge flap (V) and defines its extending movements, wherein the length and the mutual position of the levers (a, b, c) and the curvature of the main wing nose (N) are matched to one another such that during a first part of the extending movement from the retracted position (I) to an intermediate position (II) the trailing edge (K) of the leading-edge flap (V) substantially blocks the gap (g) between the leading-edge flap (V) and the main wing (H) and that during a further part of the extension movement following the intermediate position (II), the trailing edge (K) of the leading-edge flap increasingly exposed the gap (g).