To provide a movable sheath with the expandable side wall for inserting a colonoscope, which facilitates insertion of a colonoscope and allows deep insertion of the colonoscope to the ileum and the jejunum.

The movable sheath with the expandable side wall for inserting colonoscope is designed to have a sheath cylinder 1 which has a hollow side wall, is connected with an injection tube 3, and is provided with the expandable side walls 4 that is expanded and contracted by a pressure of air or oil transferred through the injection tube 3. The expandable side walls 4 can be expanded and contracted to drive the sheath for passing the colonoscope fiber through deeper and deeper in the large intestine. The top end of the colonoscope fiber is provided with a ring stopper to prevent the sheath from driving forward from the top end of the colonoscope fiber, thereby to drive the colonoscope fiber also deeper and deeper together with the sheath, facilitating insertion and allowing deep insertion of the colonoscope to the ileum and the jejunum. The sheath can be connected with the injection tube 3 to increase a propulsive force. The inner can be constructed to block from the outer to maintain its hygiene.