An insertion instrument includes a rotating member rotatable around a rotation axis, and adjacent portions adjacently provided on both sides of the rotating member in the direction along the rotation axis. The insertion instrument includes a cover tube forming a part of an outer surface of an insertion section and provided in an elastic deformation state so as to apply elastic force toward an inner peripheral side of the insertion section. A position of the rotating member in the direction along the rotation axis is adjusted by the elastic force, whereby a state where both ends of the rotating member in the direction along the rotation axis are located apart from the adjacent portions is maintained.
