A method of treating hydrogen sulfide or producing hydrogen which comprises disposing a liquid tank having a photocatalyst electrode comprising a photocatalyst and a liquid tank having a metal electrode so that the two liquid tanks are separated from each other by a cation-exchange membrane, placing a liquid containing either hydrogen sulfide or an organic substance in the liquid tank having the photocatalyst electrode, electrically connecting the photocatalyst electrode to the metal electrode, and exposing the photocatalyst to a light. The liquid to be placed in the liquid tank having the metal electrode preferably is an acidic solution. The photocatalyst preferably comprises a metal sulfide, and preferably is fine particles having a layered nanocapsule structure.