A guide wire (10, 70, 80, 120, 130, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380) for guiding a tubular dilator that is inserted into a living body, comprising: a flexible and elongated shaft portion (11, 350, 370); a puncture portion (15, 121, 295) located in a distal portion of the shaft portion (11, 350, 370) so as to form a hole in a biological tissue; and a stretchable deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) for covering the puncture portion (15, 121, 295), characterized in that said deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 3390) is configured such that if the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) is exposed from the dilator, the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) covers the puncture portion (15, 121, 295), a distal end of the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330,390) is located on a distal side from the puncture portion (15, 121, 295), and said deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 3390) is configured such that in a state where the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) is accommodated in the dilator, the distal end of the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) receives a force acting toward a proximal side by coming into contact with the biological tissue, and thereby, the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) elastically shrinks in an axial direction so as to expose the puncture portion (15, 121, 295). a flexible and elongated shaft portion (11, 350, 370); a puncture portion (15, 121, 295) located in a distal portion of the shaft portion (11, 350, 370) so as to form a hole in a biological tissue; and a stretchable deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) for covering the puncture portion (15, 121, 295), characterized in that said deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 3390) is configured such that if the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) is exposed from the dilator, the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) covers the puncture portion (15, 121, 295), a distal end of the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330,390) is located on a distal side from the puncture portion (15, 121, 295), and said deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 3390) is configured such that in a state where the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) is accommodated in the dilator, the distal end of the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) receives a force acting toward a proximal side by coming into contact with the biological tissue, and thereby, the deformation portion (30, 71, 81, 90, 100, 110, 150, 170, 190, 210, 230, 250, 270, 290, 310, 330, 390) elastically shrinks in an axial direction so as to expose the puncture portion (15, 121, 295).