A light scanning device comprising: - at least one light source including a plurality of light-emitting elements (32a, 32b, 32c, 32d) located at intervals one another in a predetermined direction; - a deflector configured to deflect so to scan by reflecting a plurality of light beams, the plurality of light beams being emitted from the respective light-emitting elements (32a, 32b, 32c, 32d); - a reflection mirror located in an optical path between the at least one light source and the deflector, the reflection mirror configured to guide the plurality of light beams emitted from the plurality of light-emitting elements (32a, 32b, 32c, 32d) to the deflector; and - a light width regulating portion configured to regulate widths of the plurality of light beams reflected by the reflection mirror in a main-scanning direction, characterized in that the light width regulating portion is located adjacent to a reflecting surface of the reflection mirror and includes a pair of regulating wall portions located opposed one another in the main-scanning direction, wherein the pair of regulating wall portions is secured to the reflection mirror to be unitized, and wherein the light width regulating portion further comprises perpendicular wall portions and inclined wall portions, that are integrally located on the respective regulating wall portions, wherein the perpendicular wall portions are perpendicularly connected to the surfaces, which are outside the optical paths, of the pair of regulating wall portions, and the inclined wall portions are connected to end portions of the perpendicular wall portions, said end portions being located opposite to the regulating wall portion sides, and wherein the inclined wall portions are inclined toward the outside of the optical paths as they separate away from the reflecting surface of the reflection mirror. - at least one light source including a plurality of light-emitting elements (32a, 32b, 32c, 32d) located at intervals one another in a predetermined direction; - a deflector configured to deflect so to scan by reflecting a plurality of light beams, the plurality of light beams being emitted from the respective light-emitting elements (32a, 32b, 32c, 32d); - a reflection mirror located in an optical path between the at least one light source and the deflector, the reflection mirror configured to guide the plurality of light beams emitted from the plurality of light-emitting elements (32a, 32b, 32c, 32d) to the deflector; and - a light width regulating portion configured to regulate widths of the plurality of light beams reflected by the reflection mirror in a main-scanning direction, the light width regulating portion is located adjacent to a reflecting surface of the reflection mirror and includes a pair of regulating wall portions located opposed one another in the main-scanning direction, wherein the pair of regulating wall portions is secured to the reflection mirror to be unitized, and wherein the light width regulating portion further comprises perpendicular wall portions and inclined wall portions, that are integrally located on the respective regulating wall portions, wherein the perpendicular wall portions are perpendicularly connected to the surfaces, which are outside the optical paths, of the pair of regulating wall portions, and the inclined wall portions are connected to end portions of the perpendicular wall portions, said end portions being located opposite to the regulating wall portion sides, and wherein the inclined wall portions are inclined toward the outside of the optical paths as they separate away from the reflecting surface of the reflection mirror.