It is to provide a novel compound useful for preventing and/or treating diseases that involves 11²-hydroxysteroid dehydrogenase 1, particularly diabetes, insulin resistance, diabetes complication, obesity, dyslipidemia, hypertension, fatty liver, or metabolic syndrome. It is an 1-adamantyl azetidin-2-one derivative represented by the following general formula (1) or salt thereof, or their solvate. [wherein A ring represents C 6 - 10 aryl group, 5- to 14-membered heteroaryl group, R 1 is a hydrogen atom, halogen atom, C 1-6 alkoxycarbonyl group, hydroxyl group, carboxyl group or carbamoyl group； R 2 and R 3 are the same or different and are a C 1-6 alkyl groups R 4 , R 5 , and R 6 are same or different, and are a hydrogen atom, halogen atom, C 1-6 alkyl group, C 1-6 alkoxy group, C 6-10 aryl group, or R 4 and R 5 , or R 5 and R 6 may together form a C 1-3 alkylenedioxy group, R 7 and R 8 are the same of different and represent a hydrogen atom or C 1 - 6 alkyl) group, or may together form a C 3-6 cyclic hydrocarbon group, n represents an integer of 0 or 1]
