A compound represented by the formula (I): wherein R 1 is a monocyclic nitrogen-containing heterocyclic group optionally condensed with a benzene ring or a heterocycle, the monocyclic nitrogen-containing heterocyclic group optionally condensed with a benzene ring or a heterocycle optionally has substituent(s), R 2 is an optionally substituted C 6-14 aryl group, an optionally substituted thienyl group or an optionally substituted pyridyl group, R 3 and R 4 are each a hydrogen atom, or one of R 3 and R 4 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 R 5 is an alkyl group, or a salt thereof, for use for the treatment or prophylaxis of peptic ulcer, Zollinger-Ellison syndrome, gastritis, erosive esophagitis, reflux esophagitis, symptomatic gastroesophageal reflux disease (Symptomatic GERD), functional dyspepsia, gastric cancer, stomach MALT lymphoma, or gastric hyperacidity； or the inhibition of upper gastrointestinal hemorrhage due to peptic ulcer, acute stress ulcer, hemorrhagic gastritis or invasive stress, or for use for the eradication of helicobacter pylori.本發明提供一種具有優異之酸分泌抑制作用且顯示抗潰瘍活性等之化合物。本發明提供一種式(I)所示之化合物或其鹽其中R1為視需要與苯環或雜環縮合之含氮單環狀雜環基，該視需要與苯環或雜環縮合之含氮單環狀雜環基視需要具有取代基群，R2為視需要經取代之C6－14芳基、視需要經取代之噻吩基或視需要經取代之吡啶基，R3及R4各為氫原子，或R3及R4中之一者為氫原子而另一者為視需要經取代之低碳數烷基、醯基、鹵原子、氰基或硝基，以及R5為烷基。
