A balloon catheter and a stent delivery system are disclosed, which includes a shaft portion of which an axially orthogonal cross section of an outer peripheral surface has a polygonal shape, and a balloon which is foldable on the outer peripheral surface of the shaft portion and in which turned-back portions are formed when folded. Portions formed to linearly extend along an axial direction in the turned-back portions are respectively positioned on sides of the polygonal shape. A stent can be arranged on an outer periphery of a balloon in the balloon catheter and expands in response to dilation of the balloon.
