A method for treating reflux esophagitis includes orally inserting an endoscope into a digestive canal; an esophageal side opening forming an esophageal side opening in a mucosal layer in a part of an esophagus; a tunnel forming step of introducing the endoscope between the mucosal and a muscle layer from the esophageal side opening forming a tunnel; an abdominal cavity side opening passing from the tunnel to an abdominal cavity closer to an anus; a protrusion step of a distal end portion of the endoscope passing through the tunnel from the abdominal cavity side opening into the abdominal cavity; and a stenosis forming a wrap on a part of an outer circumference of the digestive canal near the diaphragm closer to the anus using a medical instrument inserted into a channel of the endoscope in the abdominal cavity to form a local stenosis inside the digestive canal forming a wrap.