PURPOSE: To efficiently guide the light from a light source and to enable the execution of uniform irradiation with high luminance by providing the above light transmission plate with an exit light guiding means for guiding the right arriving at a light exit end in a prescribed irradiation direction near the outer side of the light exit end.

CONSTITUTION: The incident light on the light transmission plate 1 from the light source 2 arrives at the light exit end 5 after passing the inside of an optical fiber from a light incident end 4. The light is emitted from the light exit end 5 if the inclination angle θ of the light exit end 5 is large to some extent. The exit light, however, refracts at the time of emission and advances toward a peak part 8 formed by the light exit end 5 and the longitudinal side face of an optical fiber plate 3 and, therefore, this light transmission plate is provided with the exit light guiding means for directing the exit light toward the irradiation direction (arrow direction). A leading out layer 9 and a prism sheet 7 are arranged as this exit light guiding means. The light emitted from the exit end 5 is made incident on the inside of the prism sheet 7 through the leading out layer 9, is reflected therein and is emitted from the prism sheet 7 by changing its route toward the prescribed irradiation direction.