Provided is an excluder that reduces the burden on a patient and that can be arranged in the vicinity of a target organ within the body cavity during endoscopic surgery and the like. The excluder is for use in surgery, comprises a liquid-absorbing expandable material, and is characterized in that: the liquid-absorbing expandable material is formed to have a roll shape; and the roll-shaped liquid-absorbing expandable material expands within the body cavity as a result of absorbing liquid and spreads so as to have a planar shape.
