PURPOSE: To provide the light transmission plate for an edge light source type plane lamp which is formable without providing the plate with an irregular reflection layer consisting of printing patterns changed in the density of fine dots, is excellent in yield and production efficiency and has the excellent uniformity of illuminance.

CONSTITUTION: This light transmission plate 1 is used to convert the light of a linear light source arranged on its flank to a surface ray and is the light transmission plate for the edge light source type plane lamp formed by dispersing and incorporating light transmittable irregular reflection particles 12 having the refractive index at least on the surface different from the refractive index of a transparent substrate 11 into the transparent substrate 11. As a result, the light transmission plate is obtd. in the form of the transparent substrate 11 in which the irregular reflection particles are dispersed and incorporated. The light transmission plate is thus efficiently obtd. by a production system, such as injection molding system or casting polymn. system, with which mass production is easy.