The present invention provides a compound having a superior acid secretion inhibitory effect and showing an antiulcer activity and the like. The present invention provides a compound represented by the formula (I) wherein R1 is a nitrogen-containing monocyclic heterocyclic group optionally condensed with a benzene ring or a heterocycle, the nitrogen-containing monocyclic heterocyclic group optionally condensed with a benzene ring or a heterocycle optionally has substituent(s), R2 is an optionally substituted C6-14 aryl group, an optionally substituted thienyl group or an optionally substituted pyridyl group, R3 and R4 are each a hydrogen atom, or one of R3 and R4 is a hydrogen atom and the other is an optionally substituted lower alkyl group, an acyl group, a halogen atom, a cyano group or a nitro group, and R5 is an alkyl group or a salt thereof.