An insertion portion mounted tool of an insertion instrument includes: an expansion and retraction section provided on an outer circumferential side of an insertion portion so as to be movable forward and backward in a longitudinal direction, and configured to be expanded in the subject by an operation from outside of the subject to thereby be held by an inner wall of the subject; a positioning portion that defines a range in which the expansion and retraction section is movable forward and backward in the longitudinal direction with respect to the insertion portion; and a rotational movement restriction portion that restricts an angle in which the expansion and retraction section is rotationally moved in an outer circumferential direction on an outer circumference of the insertion portion.