PROBLEM TO BE SOLVED: To provide a medicine that prevents the occurrence of gastroesophageal reflux disease, which cannot be treated by existing treatment, prevents the recurrence thereof, provides treatment thereof, and improves its symptom.SOLUTION: In this invention, 4-[({6-[isobutyl(1,3-thiazole-2-ylsulfonyl)amino]-2,3-dihydro-1H-indene-5-yl}oxy)methyl]-3-methylbenzoic acid, its salt or prodrug is useful for preventing the occurrence of gastroesophageal reflux disease, preventing the recurrence thereof, providing treatment thereof, and improving its symptom.【課題】既存治療で効果がない胃食道逆流症の予防もしくは再発予防、治療またはその症状を改善する薬剤を提供する。【解決手段】４－［（｛６－［イソブチル（１，３－チアゾール－２－イルスルホニル）アミノ］－２，３－ジヒドロ－１Ｈ－インデン－５－イル｝オキシ）メチル］－３－メチル安息香酸、その塩またはそのプロドラッグが、胃食道逆流症の予防もしくは再発予防、治療またはその症状改善に有効である。【選択図】図３
