A stent delivery system is configured so that its outer diameter can be reduced when the balloon is folded and the stent is mounted on the folded balloon. The stent delivery system includes a balloon which is expandable by injection of fluid inside the balloon, and is folded in the form of stacked layers around an outer circumference of an elongated inner tube. The stent delivery system also includes a stent having a plurality of annular parts, each formed with a wire in an annular shape and arranged in the direction of the axis of the stent, and a plurality of connecting parts connecting the neighboring annular parts. All the connecting parts are arranged on the outer circumference of the balloon in a manner that each of the connecting parts is positioned on a minimum-layered portion having the smallest number of stacked layers.
