Provided are a scanning optical apparatus including an incident optical system for guiding a light beam emitted from a light source unit to a deflecting unit, an imaging optical system for imaging, on the surface to be scanned, a light beam deflectively scanned by the deflecting unit, and an optical path changing unit which is provided on an optical path between the deflecting unit and the surface to be scanned and includes at least two optical path changing elements. One of an optical path changing element having a minimum reflectance has a reflectance equal to or smaller than 70% in all areas used for image formation. An on-axis light beam deflected by the deflecting unit enters the optical path changing element having the minimum reflectance at a minimum angle of the at least two optical path changing elements.