A guide wire, a medical device, and a medical method are able to achieve satisfactory workability and while ensuring safety by preventing a puncture needle portion from performing erroneous puncture. A guide wire for guiding a dilator to be inserted into a living body includes a shaft portion, a puncture portion fixed to a distal portion of the shaft portion, and whose distal side includes a needle portion for forming a hole in a biological tissue, and a deformable deformation portion fixed to the shaft portion or the puncture portion. The deformation portion located inside the dilator restricts deflection of the distal portion of the shaft portion.