In the treatment method of the present invention, the operation is performed in the following steps: an apparatus is perorally inserted in the stomach, a distal end portion of the apparatus inserted in the stomach is introduced from the stomach into the peritoneal cavity, a membrane of part of the outer wall of the abdominal esophagus is removed by the distal end portion of the apparatus which is introduced in the peritoneal cavity, the distal end portion of the apparatus which is introduced in the peritoneal cavity is returned therefrom into the stomach, the stomach fundus is perorally pulled to the part of the outer wall of the abdominal esophagus, and the pulled stomach fundus is fixed to the part of the outer wall of the abdominal esophagus.