A light guide includes an incident surface, an exit surface and a reflective surface. The reflective surface is located opposite to the exit surface to extend in the main scanning direction and includes a plurality of light reflecting patterns formed to reflect the incident light toward the exit surface. The light reflecting patterns have an oval hemispherical shape rising toward the exit surface and a first diameter of the oval hemispherical shape along a sub-scanning direction is equal to or longer than a second diameter thereof along the main scanning direction. The light reflecting patterns are formed to vary the ratio of the first diameter to the height of the oval hemispherical shape depending upon the location on the reflective surface in the main scanning direction.