A guide wire (1) includes a core portion (2A) formed of an elongated object having flexibility, in which the core portion (2A) includes a main body portion (3) formed on a proximal side, a flat plate portion (5) formed on a distal side, and a transition portion (4) which connects the main body portion (3) and the flat plate portion (5), and in which at least one groove portion extending in a direction different from a length direction is formed on a slope of the transition portion (4) in the length direction. In addition, the guide wire (1) includes a coil portion (6) disposed so as to cover the distal side of the core portion (2A).
