An optical radiation device includes a long light source unit in which light emitting elements are arranged in array, a long substrate on which the light source unit is mounted, a long optical guide to guide the light beams from the light emitting elements to a predetermined plane, and an optical collector to collect the light beams reflected by the predetermined plane. The length of an effective read area from a reading center of the optical collector to one end of the predetermined plane is different from that of an effective read area from the reading center to the other end thereof. The optical guide formed by injection molding includes a gate at one end in a length direction and a surface at the other end to exert total reflection, and is disposed so that the gate is positioned on the a same side as a shorter effective read area.