To provide a tyrosinase inhibitor which is obtained from a natural raw material, inhibits the activity of the tyrosinase to suppress the production of melamine, little produces side effects, and is useful as a bleaching ingredient, and to provide a new external preparation for skins, which contains an ingredient obtained from a natural raw material, has a tyrosinase-inhibiting function, and is useful as a cosmetic and the like.

This tyrosinase inhibitor is characterized by containing as an active ingredient a black soybean skin extract composition extracted from black soybean skins. The external preparation for skins is characterized by containing as an active ingredient a black soybean skin extract composition extracted from black soybean skins. The black soybean skin extract composition is a composition obtained by extracting the black soybean skins with acidic water, and then subjecting the extract to a concentration treatment, a neutralization treatment and a desalting and concentration treatment using an ultrafiltration membrane. It has experimentally been confirmed that the water-soluble ingredient eluted by the water extraction of the black soybean skins exhibits the tyrosinase-inhibiting effect. The tyrosinase inhibitor and the external preparation for skins, which contain the black soybean skin extract compositions as the active ingredients, exhibit good bleaching actions, respectively.