The present invention provides a heterocyclic compound represented by the following formula (I), which has a glucagon antagonistic action and is useful for the prophylaxis or treatment of diabetes and the like, a compound represented by wherein ring A is an optionally substituted benzene ring and the like； Y is a nitrogen atom and the like； X is -O- and the like； R 4 is a hydrogen atom and the like； R 5 and R 6 are each independently a hydrogen atom and the like； R 1 is an optionally substituted hydrocarbon group and the like； R 2 is a hydrogen atom and the like； and R 3 is -(CH 2 ) 3 -COOH and the like, or a salt thereof.
