An area light source device has a light guide plate having a light incident surface and a light exit surface, wherein the light guide plate spreads light introduced from the light incident surface to substantially the entire light exit surface, and exits the light to outside from the light exit surface, and a linear light source arranged facing the light incident surface of the light guide plate. A diffusion pattern diffuses and reflects the light in the light guide plate within a surface parallel to the light incident surface is formed on the light exit surface of the light guide plate. A deflection pattern reflects the light in the light guide plate within a plane perpendicular to the light incident surface and the light exit surface to deflect the light in a direction perpendicular to the light exit surface little by little, and diffuses and reflects the light in the light guide plate within a surface parallel to at least the light incident surface is formed on a surface on the side opposite to the light exit surface of the light guide plate.