A skin agent for external use and a cosmetic agent are provided, by transdermal administration of which expected actions and effects of ubiquinone derivatives, salts thereof, ubiquinones and ubiquinols are effectively obtained.The skin agent for external use includes a ubiquinone derivative or a salt thereof as an active ingredient. The ubiquinone derivative is represented by the formula (1):wherein R1 and R2 are each a hydrogen atom or a phosphoric group, at least one of R1 and R2 is a phosphoric group, and n is an integer in the range of 1 to 9.
