The present invention provides a bending and extending device having an advantageous structure in terms of prevention of unexpected local bending due to buckling.The bending and extending device 1 of the present invention comprises an elastic hollow guide unit 2 and a movable part 3 to be movably inserted into the guide unit 2. The movable part 3 is constituted, either partially or entirely, of a plurality of belt-like flexible parts 30a and 30b, which extend in the axial direction of the guide unit 2 and the flexible parts 30a and 30b are connected at distal ends. The bending and extending device 1 of the present invention is characterized in that, when, by the sliding operation of the flexible parts 30a and 30b, a cross-section in which a contact point T of the flexible part 30a and the inner surface of the guide unit 2 is present on an extending line Y extending from a line segment connecting the centroid P of the flexible part 30b and the axial center G of the guide unit 2 and in which the flexible part 30a and the second flexible part 30b are in contact with each other is generated, and when the cross-section is divided into two ranges by a predetermined straight line X, the centroid P of the flexible part 30b is not positioned in a range in which the contact point T is present； and the predetermined straight line X is a line that passes through the axial center G of the guide unit 2, and that orthogonally crosses the extending line Y.
