An insertion device includes an insertion section extending along a longitudinal axis, a rotor provided in the insertion section rotating around the longitudinal axis, and an assistance tool attached to the insertion section in a state to cover the rotor from an outer peripheral side. The assistance tool rotates around the longitudinal axis together with the rotor when press force is applied from a first projection of the rotor to a second projection of the assistance tool by a rotation of the rotor. An angular position of the second projection around the longitudinal axis can be recognized from an outside of the assistance tool.
