A back light device for use in a liquid crystal display device, which includes: at least one lamp; a light guide plate for guiding light emitting from the lamp; a diffusing sheet for diffusing light emitting from the light guide plate; at least one prism sheet located on the diffusing sheet, concentrating light; a protecting sheet located on the prism sheet; and a reflector located under the light guide plate, reflecting light directing downward the light guide plate. At least one of an edge portion of the diffusing sheet adjacent to the lamp, an edge portion of the protecting sheet adjacent to the lamp, and the reflector includes a printing portion made of colorless ink containing a light scattering agent.