An object of the present invention is to provide a safe and highly effective insulin resistance improving agent or therapeutic agent for type II diabetes. According to the present invention, an insulin resistance improving agent or a therapeutic agent for type II diabetes comprising a compound represented by general formula (I) (wherein R1, R2, and R3 are the same as or different from each other, and each represents lower alkyl, lower alkenyl, lower alkynyl, aralkyl, araryl, phenyl, or a hydrogen atom) or a salt thereof as an active ingredient can be provided.