Disclosed is a compound represented by the formula (1) below, a prodrug thereof or a pharmaceutically acceptable salt of either, which is useful as a therapeutic, preventive or ameliorating agent for diabetes and the like. (In the formula, R3 represents an optionally substituted carbamoyl group or the like; X represents a hydroxyl group or the like; W1 and W2 independently represent a single bond or methylene; R7 and R8 independently represent a hydrogen atom, an optionally substituted alkyl group or the like; and Ar represents an optionally substituted aryl group or the like.)