PROBLEM TO BE SOLVED: To provide an endoscope insertion assisting instrument, by which when an operator changes orientation of a subject, the operator can operate an endoscope at the operators side before the change without moving to the orientation.SOLUTION: The endoscope insertion assisting instrument includes: a mouthpiece 8 mounted on the mouth of the subject 130 a bent cylindrical part 9 that is bent and extended from the mouthpiece 8 and a cap 3 that is extended from the bent cylindrical part 9 toward an end opening 18 and whose inner diameter is gradually increased toward the end opening 18.
