It is to provide a novel compound useful for preventing and/or treating diseases that involves 11β-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 C6-10 aryl group, 5- to 14-membered heteroaryl group, R1 is a hydrogen atom, halogen atom, C1-6 alkoxycarbonyl group, hydroxyl group, carboxyl group or carbamoyl group; R2 and R3 are the same or different and are a C1-6 alkyl group; R4, R5, and R6 are same or different, and are a hydrogen atom, halogen atom, C1-6 alkyl group, C1-6 alkoxy group, C6-10 aryl group, or R4 and R5, or R5 and R6 may together form a C1-3 alkylenedioxy group, R7 and R8 are the same of different and represent a hydrogen atom or C1-6 alkyl group, or may together form a C3-6 cyclic hydrocarbon group, n represents an integer of 0 or 1].