The guide tube for forming a pneumoperitoneum of the present invention comprising a flexible tube having an inner cavity, has an outer diameter that allows the guide tube to be inserted into a puncture needle, a distal end of the guide tube is closed, the distal end is provided with a tip portion that can be held by holding forceps provided in an endoscope, a proximal end of the guide tube is provided with a connecting portion to an insufflation apparatus, and the guide tube is provided with a side hole region having at least one side hole that can establish communication between the inner cavity of the flexible tube and the outside in a case where the inner cavity is pressurized through insufflation. According to the guide tube for forming a pneumoperitoneum of the present invention, only with single puncture from the body surface into the lumen of a lumen organ, a preliminary pneumoperitoneum can be safely and reliably created without damaging other organs, and, at the same time, the part of the lumen organ wall pierced during formation of the pneumoperitoneum can be used as a route for accessing the peritoneal cavity from the lumen of the lumen organ.
