A width in a main scanning direction of a laser beam is decreased in the outside of an effective scanning region in such a manner that the width along the main scanning direction of the laser beam is restricted by an aperture portion of an aperture member. As a result, so-called flare light is prevented from generating, and a uniformity of light quantity is improved. Namely, in a light scanning apparatus adopting an overfilled optical system, a light scanning apparatus which can prevent degradation of image quality due to flare light is obtained.