To provide a treatment sheath providing for good operability of an endoscope of suction tube during insertion, and enabling a lesion area around the inserted portion of the sheath to be treated without the need to move the sheath inserted in a coelom and the need to take out the endoscope or treatment tool inserted in the sheath.

The treatment sheath is provided with a treatment hole moving means 24 for moving the position of an opening 23 at an overlap between a spiral second slit 22 in an inner cylinder member 10 and an approximately rectilinear first slit 19 in an outer cylinder member 9 by rotating an operating end portion 12 of the inner cylinder member 10 relative to the outer cylinder member 9 to cause relative rotation between the outer cylinder member 9 and the inner cylinder member 10.