PURPOSE: To provide a light transmission plate device where a part of irregularly reflected light at a pressure sensitive adhesive part is emitted to the outside of a light transmission plate, abnormal light emission is prevented, luminance at an effective light emitting surface is not lowered and the unevenness of luminance is avoided.

CONSTITUTION: This light transmission plate device is equipped with the light transmission plate 11 whose one surface is set as the light emitting surface 11a and whose other surface is set as a reflecting surface 11b, and a bar-like light source 15 is adjacently arranged on the light introducing end face 14 of the plate 11, then a lamp reflection film 16 is arranged so that the light source 15 and the end face 14 may be covered therewith. A transparent film 19 is extended to the end of the film 16, and stuck to the side of the light emitting surface 11a of the plate 11 through the pressure sensitive adhesive part 17.