Provided is a guide sheath that is prevented from coming out of a body cavity so as to allow for stable operation. A tubular guide sheath that guides an insertion section of a medical device to be inserted into a body cavity includes a base-end opening that is provided at a base end of the guide sheath and into which the insertion section is inserted a distal-end opening that is provided at a distal end of the guide sheath a flexible bent section that is provided at the distal end of the guide sheath and is elastically bent and an exit opening that is provided in an outer side surface of the bent section and from which the insertion section extends out.
