A track-forming device can form an insertion route (track) along which a treatment tool is easily inserted. The track-forming device includes: a plurality of track-forming segmented members that are arranged in the longitudinal direction with spaces therebetween; a soft wire that connects the plurality of track-forming segmented members; and a wire pulling section that brings the plurality of track-forming segmented members into contact with each other in the longitudinal direction. When the plurality of track-forming segmented members are brought into contact with each other by the wire pulling section, a predetermined track is formed.