A shaft of a catheter is disclosed, the shaft has a thin portion, which constitutes a distal side of the shaft, a thick portion which is provided further on a proximal side than the thin portion, and a tapered portion which is provided between the thin portion and the thick portion. The tapered portion is formed more flexibly than the thick portion. The thick portion has a first thick portion and a second thick portion which is provided between the tapered portion and the first thick portion. The second thick portion has a smaller outer diameter than the outer diameter of a proximal end of the tapered portion and the outer diameter of the first thick portion, and is formed more flexibly than the first thick portion.
