Patent ID: 8368844

Claim:
An area light source device comprising: a light source; a light guide plate, wherein the light guide plate is arranged at a position facing the light source, for introducing light of the light source from a light incident end face and exiting the light to the outside from a light exit surface; wherein the light guide plate comprises: a light guide substrate made of translucent material, a low refraction index layer having a lower index of refraction than the light guide substrate, wherein the low refraction index layer being closely attached to a surface on a side opposite to the light exit surface of the light guide substrate , and a reflection layer closely attached to a surface on a side opposite to the light exit surface of the low refraction index layer; wherein the light guide substrate comprises: a light introducing section arranged at a position facing the light source, and a light guide plate main body comprising the light exit surface for exiting the light introduced from the light introducing section to the outside integrally configured; a tapered portion inclined to gradually increase the thickness of the light introducing section the farther away from the light source, wherein the tapered portion inclined is arranged on the surface on the light exit side of the light introducing section or the surface on the opposite side; a light control pattern for reflecting the light in the light guide plate main body and leaking the light towards the low refraction index layer from the surface on the side opposite to the light exit surface of the light guide plate main body, wherein the light control pattern is formed on the light exit surface side of the light guide plate main body; and a light exit unit for reflecting the light leaked to the low refraction index layer and exiting the light from the light exit surface, wherein the light exit unit is formed on an boundary of the low refraction index layer and the reflection layer or a surface on the side opposite to the boundary of the reflection layer.