A surface light source device capable of suppressing generation of bright line and preventing generation of crush of pattern forming on a light guide plate even when pressure is applied, includes a plurality of deflection patterns and diffusion patterns wherein the diffusion pattern is formed on the light source side of the deflection pattern. Further, the diffusion pattern is provided so as not to protrude outwards from the light guide plate from the plane opposite to the light-emitting plane and the diffusion pattern diffuses the light incident from a light guide direction to a direction different from the light guide direction seen from a direction perpendicular to the light emitting plane.