An image reading device, includes an illumination optical system which has a light source unit configured to emit light being illuminating light to an illuminated object; an optical member configured to have a plurality of reflecting plates and collect the light emitted from the light source unit; and a plurality of reflecting members, the light emitted from the light source unit being collected by the optical member, and the collected light being reflected by the plurality of reflecting members to illuminate a reading target area on the illuminated object, and at least one reflecting surface of the optical member or the plurality of reflecting members having a relief structure.