Bending and extending device and bending and extending method

A bending and extending device, comprising:

• an elastic hollow guide unit;
• and
• a movable part to be movably inserted into the guide unit,
• wherein:
• the movable part is constituted, either partially or entirely, of a plurality of belt-like flexible parts, which extend in the axial direction of the guide unit and are connected at distal ends;
• the movable part causes the plurality of flexible parts to be bent in the direction perpendicular to the axial direction of the guide unit by sliding one of proximal ends of the plurality of flexible parts in the axial direction of the guide unit (hereinafter referred to as a flexible part sliding operation);
• when, by the flexible part sliding operation, a cross-section in which a contact point of a second flexible part and the inner surface of the guide unit is present on an extending line extending from a line segment connecting the centroid of a first flexible part and the axial center of the guide unit and in which the first flexible part and the second flexible part are directly or indirectly in contact with each other is generated, and when the cross-section is divided into two ranges by a predetermined straight line, the centroid of the first flexible part is not positioned in a range in which the contact point of the second flexible part and the inner surface of the guide unit is present;
• and
• the predetermined straight line is a line that passes through the axial center of the guide unit, and that orthogonally crosses the extending line.