The development of agents for gastroesophageal reflux disease, in which existing treatment is not effective, is strongly demanded. An object of the present invention is to provide an agent for preventing or relapse-preventing, treating or ameliorating such gastroesophageal reflux disease. 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.
