Abstract: A compound represented by general formula (I-2) or a pharmaceutically acceptable acid-addition salt thereof, useful as an anti-microbial against Helicobacter pylori and as a medicinal composition for treating Helicobacter pylori infection, wherein Ar represents phenyl, biphenyl or naphthyl each having a at least one substituent selected from the group consisting of halogen, cyano, nitro, carboxy, C1-C18 alkyl, C1-C18 alkoxy, C3-C18 cycloalkyl, C7-C18 aralkyl, C8-C18 arylalkenyl, C7-C18 aralkyloxy, optionally substituted phenoxy, optionally substituted C2-C19 alkoxycarbonyl, and optionally substituted C8-C19 aralkyloxycarbonyl, provided the case where Ar represents phenyl substituted by halogen, cyano, nitro, carboxy, C1-C18 alkyl, optionally substituted C2-C19 alkoxycarbonyl or C8-C19 aralkyloxycarbonyl is expected.