To prevent a bright line caused by reflection of edges from occurring and to emit irradiating light with uniform light quantity by arranging plural emission-enhancing regions with a variety of extent to promote the emission of irradiating light mixed with themselves and making the density of the plural emission-enhancing regions variable.

The first emission-enhancing regions P1 are arranged in the vicinity of the incident plane where a bright line is observed. Furthermore, the second emission-enhancing regions P2 with a relatively lower function to promote the emission of irradiating light than the first emission-enhancing regions P1 are densely arranged among the first emission-enhancing regions P1. Furthermore, the ratio of area covered with, and the unit area of the light- emitting surface 2C occupied with, the second emission-enhancing regions P2 gradually get lower as it goes farther away from the vicinity of the incident plane. Thus, the part where a bright line is prevented from occurring is made less conspicuous. In this case, the first and the second emission-enhancing regions P1 and P2 are formed in dimensions difficult to be visible.