The invention discloses an optical scanning apparatus and an image forming apparatus. An optical scanning apparatus includes: a light source that emits multiple light beams; a deflecting unit that accepts the multiple light beams emitted from the light source on an identical reflecting surface of the deflecting unit, and movies the reflecting surface to deflect the multiple light beams; and an optical system that is interposed between the reflecting surface of the deflecting unit and a surface to be scanned and converges the multiple light beams reflected by the reflecting surface respectively. And the optical system includes an optical element that converges lights at least in a sub scanning direction. The optical scanning apparatus includes an adjust unit that adjusts incident angles of the multiple light beams radiated onto the optical element, in a direction corresponding to the sub scanning direction on the surface to be scanned.