Light-diffusing-member manufacturing method and manufacturing device

A light-diffusing-member manufacturing method comprising:

• a step of forming a light shielding layer on one surface of a base with optical transparency;
• a step of forming a negative photosensitive resin layer with optical transparency so as to cover the light shielding layer on the one surface of the base;
• a step of exposing the negative photosensitive resin layer by irradiating the negative photosensitive resin layer with ultraviolet light, from a surface on an opposite side of the one surface of the base having the light shielding layer and the negative photosensitive resin layer formed therein, through the base at a region other than a region having the light shielding layer formed therein;
• a step of forming a light diffusion portion having a light-emitting end surface on the base side, and having a light incident end surface of a larger area than the area of the light-emitting end surface on the opposite side of the base side, on the one surface side of the base, by developing the negative photosensitive resin layer with an alkali developing solution, after the exposure;
• and
• a step of performing an acid treatment on the light diffusion portion with an acid solution, after removing the alkali developing solution which is adhered to the light diffusion portion and suspended matter in the alkali developing solution in the negative photosensitive resin layer, so as to lower an ionization degree of the negative photosensitive resin layer which is in an ionized state due to the alkali developing solution.