ILLUMINATION DEVICE, IMAGE READING DEVICE, AND IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide an illumination device capable of eliminating scattering of light in a light guide body to suppress reduction in lighting efficiency, an image reading device, and an image forming apparatus.SOLUTION: A plurality of positioning projections 21 are integrally formed with a lower surface 13d of a light guide body 13 along a main scanning direction. Each of the positioning projections 21 is fitted to each of fitting holes 22 formed on a lower side holding plate 18, so as to position and fix the light guide body 13 inclined by a predetermined angle on the lower side holding plate 18 so that an emission surface 13b is directed to a document reading area G1 side. In order to prevent, of light beams from an LED light source 12 entered from an incidence surface 13a to the light guide body 13, light beams totally reflected at positions of the respective positioning projections 21 of the lower surface 13d, guided in the light guide body 13, and emitted from the emission surface 13b, from directly reaching the document reading area G1, at least the respective positioning projections 21 are formed closer to the incidence surface 13a than an intermediate position between the incidence surface 13a and the emission surface 13b of the lower surface 13d.