A light scanning apparatus is provided. The light scanning apparatus includes a beam splitter, which is located between a polygonal mirror and an f.theta. lens and reflects a portion of light incident thereon to the polygonal mirror. A laser beam reflected from the beam splitter is reflected by the polygonal mirror and incident on the f.theta. lens. The path of a laser beam incident on the polygonal mirror and the path of the laser beam reflected from the polygonal mirror are at the same level with each other. Therefore, by installing a beam splitter in a laser scanning apparatus, it is possible to reduce the length of each reflective surface of the polygonal mirror in a main scanning direction without increasing the length of each reflective surface of the polygonal mirror in a sub scanning direction. In addition, it is possible to perform high-speed scanning while making less noise.