A compound represented by the following formula (1) or a salt thereof: ##STR1##

wherein R¹ represents a C_1-12 alkyl group, phenyl group, 1-naphthyl group and the like, R² represents a C_2-12 alkyl group, (R³)_b represents 0 to 4 substituents such as a halogen atom, R⁴ represents a lower alkyl group, R⁵ represents hydrogen atom or a lower alkyl group, n represents an integer from 2 to 4, and X represents —NH— or —O—, which has superior hypoglycemic action, hypolipidemic action and total cholesterol reducing action, and is useful as an active ingredient of a medicament for prophylactic and/or therapeutic treatment of diseases including diabetes mellitus, hyperlipidemia and the like.