PROBLEM TO BE SOLVED: To provide an assembly or the like non-invasive to a patient, not complicated and capable of shortening the operation time, and guiding a sheath and a dilator without damaging an opening of a Wharton tube and the inner wall of a lumen without making the position of the opening unknown in the midway.SOLUTION: In an assembly 40, a sheath 10, a hollow dilator 20 inserted in the sheath 10 and a stylet (an insertion instrument) 30 inserted in the dilator 20 are integrated with each other. When a connector part 24 of the dilator 20 is fitted in a connector part 14 of the sheath 10, the tip B of the dilator 20 is projected from the tip A of the sheath 10 by a predetermined length (9 mm). When a connector part 34 of the stylet 30 is fitted in the connector part 24 of the dilator 20, the tip C of the stylet 30 is projected from the tip B of the dilator 20 by a predetermined length (7 mm). The dilator 20 and the stylet 30 are integrated with each other to be removed from the inside of the sheath 10 while fitting is kept.
