Now it is strongly desired to develop a drug for the gastroesophageal reflux disease for which the existing treatments is ineffective. An object of the present invention is to provide a drug for prevention or relapse prevention, treatment or improvement of such symptom of gastroesophageal reflux disease. The prevent invention provides 4-[({6-[isobutyl-(1,3-thiazol-2-yl sulfonyl)amino]-2,3-dihydro-1H-inden-5-yl}oxy) methyl]-3-methylbenzoic acid, a salt thereof or a pro-drug thereof, which is effective in prevention or relapse prevention, treatment or improvement of symptom of gastroesophageal reflux disease.目前強烈期望開發出針對既存治療無效之胃食道逆流症的藥劑。本發明之課題係提供此種胃食道逆流症之預防或預防再發、治療或改善症狀之藥劑。解決上述課題之手段為4-[({6-[異丁基(1,3-噻唑-2-基磺醯基)胺基]-2,3-二氫-1H-茚-5-基}氧基)甲基]-3-甲基苯甲酸、其鹽或其前驅藥，其係對於胃食道逆流症之預防或預防再發、治療或改善症狀為有效。
