A guide wire is disclosed, which includes a core portion formed of an elongated object having flexibility, in which the core portion includes a main body portion formed on a proximal side, a flat plate portion formed on a distal side, and a transition portion which connects the main body portion and the flat plate portion, 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 in the length direction. In addition, the guide wire includes a coil portion disposed so as to cover the distal side of the core portion.
