There is provided a light beam scanning apparatus which deflects a light beam from a light source by using a deflector and scans the surface of a photosensitive member with a focused light beam. The light beam scanning apparatus includes a first electro-optical element placed on the optical axis of the light beam between the light source and the deflector. The first electro-optical element includes an electro-optical crystal and transparent electrodes respectively provided on surfaces of the electro-optical crystal which oppose each other in the optical axis direction.