LIGHT GUIDE BODY AND SURFACE LIGHT SOURCE DEVICE

PROBLEM TO BE SOLVED: To provide a light guide body which facilitates application of local dimming in the edge light type surface light source device.SOLUTION: A light guide body for an edge light type surface light source device has: a light incident edge surface 31; and a light emission surface 33 and a back surface 34 which are substantially vertical to the light incident edge surface and are located on sides opposite to each other. A directional light emission function part composed of a lens array formation surface on which a lens array 33' and a lens array 34' are formed in parallel is applied onto surfaces of both of the light emission surface 33 and the back surface 34. The lens array 33' and the lens array 34' are extended with an inclination angle of 9° or less on sides opposite to each other with respect to the normal direction of the light incident edge surface 31. In the lens array 33' and the lens array 34', cross-section vertical to the extension direction has a shape of a convex curve or a shape formed by assembling straight lines to both edges of the convex curve. When an array pitch of the lens array 33' and the lens array 34' is P and a height thereof is h, a relational expression of 0.4×P≤h is satisfied.