It is to provide a novel compound useful for preventing and/or treating diseases that involves 11²-hydroxysteroid dehydrogenase 1 (in particular diabetes, insulin resistance, diabetes complication, obesity, dyslipidemia, hypertension, fatty liver, or metabolic syndrome). [Means to solve the object] A 1,2-diazetidin-3-one derivative represented by the following general formula (1) or salt thereof, or their solvate.