To prevent the function of a photocatalyst functioning body from being deteriorated even when used for a long time by contacting the photocatalyst functioning body, which is formed from optical semiconductor powder, silicon fine particles and an adsorption material, with water in an ultraviolet ray irradiating step.

The photocatalyst functioning body 1 is formed from the optical semiconductor powder 2 such as TiO2, CdS, CdSe, WO3, Fe2O3, SrTiO3 and KNbO3, the silicon fine particles 3 functioning as an electrode and one or more adsorption materials 4 selected from the group consisting of ceramic powder such as apatite (phosphorite), zeolite and cebollite, activated carbon and a silk fiber-containing material. The body 1 is brought into contact with water in the ultraviolet ray irradiating step for irradiating the water with plural ultraviolet rays of selected wavelengths individually. Thereby, the function of the body 1 can be enhanced even when used for a long time.