PROBLEM TO BE SOLVED: To provide a mouthpiece for an endoscope that facilitates the visual field development of lower larynx in a state where the mouthpiece is attached when using Valsalva method.SOLUTION: A mouthpiece for an endoscope 100 comprises a cylinder part for the insertion of an endoscope, and a flange part for deaeration blockage that extends from the periphery of the cylinder part.