To provide a manufacturing method for manufacturing easily a light guide plate of which one surface emits light in uniform brightness.

A surface light-emitting body 1 is provided with a transparent light guide plate 10 of rectangular shape and a light source 11 arranged on one end face of the light guide plate 10. Further, a plurality of dot grooves 21 of truncated cone shape are formed on the rear face (lower side face of the figure) of the light guide plate 10. Each of the dot grooves 21 is formed to become deeper the further it is separated from the light source 11. Accordingly, light having entered into the light guide plate 10 from the light source 11 is diffused the more the further it is separated from the light source 11, therefore, the front surface (upper surface of the figure) of the light guide plate 10 emits light in uniform brightness. Then, these dot grooves 21 are formed in those portions by laser beams of an output corresponding to the concentration of each portion based on image data corresponding to the front face of the light guide plate 10 which has a specific gradation. Therefore, the light guide plate 10 emitting light in uniform brightness can be manufactured easily.