The present invention solves various problems associated with conventional external preparations used for ameliorating skin diseases which have been issues of concern. The purpose of the present invention is to provide an external preparation, such as a cosmetic, a drug and a quasi-drug, which contains, as an active ingredient, a novel compound or the like, wherein the novel compound exhibits an activity of reducing free radicals in the skin, an anti-wrinkling activity, an anti-acne activity, a skin-moisturizing activity, a barrier function-enhancing activity and an activity of preventing ultraviolet ray-induced inflammations and is stable and safe. The external preparation has a potent skin-whitening activity, a potent activity of reducing free radicals in the skin, a potent anti-wrinkling activity, a potent anti-acne activity, a potent skin-moisturizing activity, a potent barrier function-enhancing activity, a potent activity of preventing ultraviolet ray-induced inflammations and a potent anti-decubitus activity, is mildly irritable and highly safe, and is useful as a cosmetic, a quasi-drug, a drug, a food additive, a feed additive, a veterinary drug and a drug for aquatic animals.
