In one embodiment of an optical scanning apparatus, a light blocking member is provided that is disposed facing a reflective face of a polygon mirror near the reflective face, and blocks stray light without blocking light in an effective scanning range of a laser beam. The light blocking member includes a light blocking plate having an opposing face that faces the reflective face of the polygon mirror, a support plate that supports the light blocking plate, and a fixing plate that fixes the lower edge portion of the support plate to a support member. The opposing face of the light blocking plate is inclined relative to the reflective face of the polygon mirror, and a space below the light blocking plate is open.