A light guide plate, produced from material transparent to visible light, includes a plurality of prisms provided on one surface (a diffusion surface) thereof in a predetermined pattern. The plurality of prisms include a reflection surface that reflects visible light emitted from a light source and entering the light guide plate from an input surface toward another surface (an output surface). Each prism in the plurality of prisms is distributed so that the reflection surfaces of two prisms separated by a predetermined pitch are oriented in the same direction, and the reflections surfaces of two prisms that are closer than the predetermined pitch are oriented in mutually different directions.