An intraluminal endoscope inserting method according to the present invention is a method of forming a first opening in a wall of a first luminal organ while observing optical and ultrasonic images formed by an ultrasonic endoscope inserted into a first luminal organ through a natural opening, forming a second opening in a wall of a desired second luminal organ adjacent to the first luminal organ through an abdominal cavity space from the first opening, leading the ultrasonic endoscope into a second luminal organ from a second opening and performing observation and treatment, and after the treatment and the like, stitching the openings. This makes it possible to insert the endoscope with a skill same as that required for a normal endoscope test and makes it easy to insert the endoscope even into luminal organs irregularly connected to with one another in a body cavity.