The prism sheet can minimize omission using directional sheet such as, and provides a light guide plate capable of securing a viewing angle without reducing the brightness in the vertical direction. Edge light type is a light guide plate 1 used in the surface light source device 10. Emission surface 6 has opposing bottom surface 7 and the exit surface 6 and the incident end face 8 to be incident the light emitted from the primary light source 4 provided on the side surface between the bottom surface 7 on the emission surface 6. Each includes a ridge and / or concave pattern formed at a predetermined pitch on the emission surface 6 and a bottom 7. Formed on the exit surface 6 pattern formed on the bottom surface 6 as well as perpendicular to the incident end face 8 pattern is parallel to the incident end face 8. These emission surface 6 or the bottom 7, and a ridge 2 and concave stripes 3 of the trapezoidal shape of the trapezoid shape are alternately arranged. When the surface of these ridges 2 are diffusion process, it is possible to obtain an excellent light guide plate glare is less surface quality of the surface.