To enhance the insertability and prevent a subject from feeling a pain by providing a specified number or more of endless belts on the surface of a soft part extending from this side of a specified length from the tip to a control part, and holding them by a hook provided on the soft part surface.

A soft part has two or more endless belts 13 on the surface along the longitudinal direction. The length thereof is set to 105-150% of the length extended from a guide hold 16 at 0-3 cm on this side from the soft part tip and returned to the guide hole 16 in strain through a driving device in the state where the soft part is linearly held, and the endless belts are supported by a guide hook provided on the surfaced of the soft part. The guide hook has a circular form having a diameter slightly larger than that of the endless belt 13 and a corresponding inside angle exceeding 180°. The endless belt 13 sent through a guide pipe 15 within the soft part is extended to the outside of the soft part through the guide hole 16 provided 0-3 cm on this side from the soft part tip.