To provide a stent delivery system configured to prevent twisting of a strut during expansion of a stent. A balloon has a plurality of limb portions folded at a plurality of folding pleats in a deflated state. The limb portions are folded in a first circumferential direction to surround the shaft as seen from a proximal end side of an axial direction of the shaft. The strut of the stent has helical portions formed in a helical shape extending along a second circumferential direction opposite to the first circumferential direction as seen from the proximal end side of the axial direction with being centered on an axis extending along the axial direction of the shaft.
