An image reading device includes a light source member having light source portions that release light; a light guide member that has an input section facing the light source portions and to which the released light is input, and an output section outputting the input light, and that guides the light toward a predetermined radiation position; a support member supporting the light source member and the light guide member and having higher rigidity than them; a retaining member retaining the light guide member in a supported state by the support member by pressing the light guide member toward the support member; a contact section that is provided in the light guide member, comes into contact with the retaining member, and protrudes from the light guide member toward the retaining member; and a reader member receiving the light from the radiation position so as to read an image thereof.