A rigid-endoscope oversheath having a leading end, a base end, a longitudinal shaft, and a lumen into which a rigid endoscope can be inserted, the oversheath including a flow path through which fluid flows from the base end toward the leading end along the longitudinal shaft, an ejection port formed in a same plane with a leading end plane of the rigid-endoscope oversheath to eject the fluid flowing through the flow path from the leading end plane of the flow path, a peripheral portion of the port being at least partially composed of an elastic member deformable by the fluid flowing through the flow path, and a valve at least partially attached to a leading end of the flow path to openably close the leading end of the flow path.
