The disclosed technology is directed to an insertion apparatus comprises an insertion portion having a tubular body freely rotates around a longitudinal axis over an outer circumferential surface. The insertion portion is flexible and configured to be inserted into a body cavity. A drive source is configured to rotate the tubular body wherein a part of the insertion portion includes a predetermined flexural rigidity to which the tubular body being mounted thereto. The part of the insertion portion is formed of a structure that is configured in such a manner that bending of the tubular body is not caused beyond a predetermined bending angle so as to avoid stop of rotation of the tubular body by a driving force of the drive source even when an external force that intends to keep a bending shape of the body cavity is received from a wall of the body cavity in contact.
