To provide a scanning optical apparatus, not requiring a lens in a complex figure, and also, capable of eliminating the bow of a beam light even when a plurality of correcting lenses are in an identical figure.Beam light L falls on Cross section K perpendicular to Rotational axis 1a of Polygon mirror 1 at an angle of 2° or less. When such an incident angle condition is satisfied, the figure of a cross section in the sub scanning direction of Scanning lens 9 is a spherical surface figure, and also, the curvature of Incident surface 9a and Outputting surface 9b with respect to the sub scanning direction is changed according to the position in the main scanning direction. Furthermore, Correcting lens 10 is arranged in a tilted (decentered) state with respect to the light axis of Beam light L.