An intracorporeal insertion instrument includes an elongated two guide wires having a distal end portion whose cross-sectional shape is non-circular, wherein a bending habit is applied to the distal end portion, and a sheath main body provided with a plurality of lumens formed such that the guide wires are inserted from a plurality of proximal-end openings and the respective guide wires can be protruded from distal-end openings, the respective distal-end openings being formed such that the respective guide wires are prevented from rotating around axes of the guide wires in the distal end openings, and the distal end portions of the guide wires are separated from each other along protruding directions.
