Disclosed in a multi-beam optical scanning apparatus which includes a light source unit including a plurality of radiation points disposed with being spaced from each other in a main scanning direction, and a deflecting unit for deflecting a plurality of light beams radiated from the light source unit toward a surface to be scanned. Where a first radiation point is a radiation point for radiating the light beam, out of the plurality of light beams emitted from the light source unit, which reaches the farthest location from a center of a deflecting facet of the deflecting unit in the main scanning direction, a second radiation point is a radiation point for radiating another light beam, and an upstream-side external angular range is a range which lies in an angular range over which the light beam can be deflected by the deflecting unit, and which exists on an upstream side in a rotational direction of deflecting unit relative to an effective scanning angular range at the time when the light beam is deflected toward an effective scanning range on the surface to be scanned, the second radiation point is excited in the first place in the upstream-side external angular range.