The line bow phenomenon is reduced by appropriately setting the reflective surface and/or the external shape of an optical element (e.g., a toric mirror) thereby realizing approximately linear illumination of the surface of the original document that is being read. In order to do this, optical elements can be formed so that the external shape of the reflective surface of the optical element is bow-shaped. Alternatively, the optical element can be arranged so that the optical axis of the reflective surface is parallel to the axis of the light reflected from the reflective surface.