A multi-beam optical scanning apparatus including a light source including a plurality of radiation points disposed spaced from each other in a main scanning direction and in a sub-scanning direction, a rotational polygon minor for deflecting a plurality of light beams radiated from the radiation points, and an imaging optical system for imaging the plurality of light beams deflected by a deflecting facet of the rotational polygon mirror. The deflecting facet has a width in which a light beam reaching a farthest location from a center of the deflecting facet is eclipsed by an edge of the deflecting facet if emitted prior to a light beam from a second radiation point when controlled by auto-power-control. Control is performed such that the light beam from the second radiation point is radiated prior to the light beam from the first radiation point when controlled by the auto-power-control.