A light-guiding member is provided with two light source groups on its both terminals and the light-guiding board comprises two light mixing areas which have a cross section form which is symmetry for its center line, and a light outputting area between these. The light mixing areas function as an area in which the lights from each adjacent light source group are mixed and at the same time function as an area to output the mixed lights from each remote light source group. The light outputting area functions as an area to pass a part of the mixed lights from the two light source groups and at the same time functions as an area to output the rest.