PURPOSE: To attain uniform lighting and to obtain a thin device with a low cost and with high availability by gradually enlarging the size of a plane and the size of radius of curvature of the roundness of the tip of a sectional shape in plural projecting parts formed on the rear surface of a light transmission plate as away from plural light emission diodes.

CONSTITUTION: A long-sized substrate 9 placing plural aligned light emission diodes so as to be opposed to one side surface 3 of the light transmission plate 2 is arranged. Then, the size of the plane and the size of radius of curvature of the roundness of the tip of the sectional shape in plural projecting parts 8 formed on the rear surface 5 of the light transmission plate 2 are formed so as to enlarge gradually as away from plural light emission diodes 14. That is, the sizes of a reflection surface 18 decided by the size of the plane and the size of radius of curvature of the roundness of the tip in the projecting parts 8 are increased expornential functionally as away from the light emission diodes 14. Thus, since the reflected beam becomes sufficiently strong even in the position of the light transmission plate 2 far from the light emission diodes 14, the uniform lighting is obtained.