A light guide plate capable of omitting use of a directional sheet such as a prism sheet as much as possible and ensuring a viewing angle without decreasing brightness in the vertical direction. A light guide plate 1 is used for an edge-light surface illuminant device 10. The light guide plate comprises an emission plane 6, a bottom plane 7 facing the emission plane 6 and an incident end face 8 which enters light emitted from a primary light source 4 provided in a side face between the emission plane 6 and the bottom plane 7. Each of the emission plane 6 and the bottom plane 7 comprises a pattern having convex portions and/or concave portions formed at predetermined pitches. The pattern formed on the emission plane 6 is orthogonal to the incident end face 8 and also the pattern formed on the bottom plane 6 is parallel to the incident end face 8. The emission plane 6 or the bottom plane 7 comprises a trapezoidal convex portion 2 and a trapezoidal concave portion 3 which are alternately arranged. If a diffusion treatment is performed on the surface of each of the convex portions 2, the light guide plate which has reduced glare on the surface and has a superior surface quality can be obtained.