A scanning optical apparatus capable of forming a preferable image, includes a light source unit, a rotational polygon mirror having a plurality of deflection surfaces for deflectively scanning a light flux emerged from the light source unit, an incident optical system for imaging the light flux as a line image on the deflection surfaces; and an imaging optical system which has one or more imaging lenses, images the light flux that has passed through the rotational polygon mirror on a surface to be scanned, and brings the deflection surfaces and the surface to be scanned into a conjugate relationship with each other in a sub scanning section, in which at least one of the imaging lenses of the imaging optical system has a lens surface formed into a non-arcked shape in the sub scanning section, and is held by a holding member so as to be movable.