The present invention provides an agent for preventing or relapse-preventing, treating or ameliorating gastroesophageal reflux disease, in which existing treatment is not effective.4-[({6-[Isobutyl(1,3-thiazol-2-ylsulfonyl)amino]-2,3-dihydro-1H-inden-5-yl}oxy)methyl]-3-methyl benzoic acid, a salt thereof or a prodrug thereof is effective in the prevention or relapse prevention, treatment or amelioration of gastroesophageal reflux disease.
