PROBLEM TO BE SOLVED: To provide a mouthpiece for an endoscope that facilitates the visual field development of lower larynx when using Valsalva method.SOLUTION: A mouthpiece for an endoscope 100 comprises a cylinder part for the insertion of an endoscope, and a valve part for the penetration of the endoscope and the blockage of aeration between the endoscope and the inner wall of the cylinder part. The valve part and the cylinder part are formed as separate bodies, and the valve part is detachably attached to the cylinder part.