The present invention provides an image reading device in which light guiding paths can be formed in a simple structure and adjustment of irradiation position of light irradiated onto the original is easy, including: a luminescence portion; a light guiding body including a first light incidence portion disposed on a luminescence portion side and a first light emission portion disposed on an original side; a first reflective surface connecting the first light incidence portion and the first light emission portion in the light guiding body; a light guiding space constitutive member including a second reflective surface facing the first reflective surface; a light guiding space formed between the first reflective surface and the second reflective surface, having a second light incidence portion disposed on an illumination portion side and a second light emission portion disposed on the original side; a mirror; an imaging lens; and a reading portion.