PROBLEM TO BE SOLVED: To provide a composition for external use having excellent active oxygen-eliminating effect, tyrosinase inhibitory effect and reducing effect, and becoming a skin preparation for external use or a cosmetic, having an anti-aging action by antioxidation effect and a whitening action by tyrosinase inhibitory effect, a hair cosmetic preventing the damage of the hair, further a permanent wave agent, curling agent and wavy hair-correcting agent by the reducing effect on disulfide bonds, and a hair dye. SOLUTION: This composition for external use is characterized by containing 1 kind or ≥2 kinds selected from 2-thiazolidine-4-carboxylic acid expressed by formula (1) or its derivative, or 2-methylthiazolidine-2,4-dicarboxylic acid expressed by formula (2) or its derivative, or their salts. COPYRIGHT: (C)2010,JPO&INPIT