Abstract: A valve and and a valved trocar jacket tube by which there is no need of an adapter, types of a clamp or the like to be used are not limited, and leakage of an inert gas from an abdominal cavity can be prevented. In the valve and the valved trocar jacket tube, when a pair of rings are relatively rotated at a predetermined angle in the opposite directions, a cylindrical section in a rubber-like member is opened. In case of employing a clamp or the like, it is inserted into the abdominal cavity through the opened cylindrical section. Since the rubber-like member has elasticity, the cylindrical section is close together with the clamp or the like inserted.