A stent delivery system includes an elongated shaft, a balloon and a stent. The balloon is dilatable from a contracted position to an expanded position when a fluid flows into an interior of the balloon. The stent is formed by wires that are spaced apart so that at least one gap is formed between the wires. The stent is mounted on the outer surface of the balloon when the balloon is contracted. The balloon includes a protruding portion which protrudes radially outward through the gap of the stent when the stent is mounted on the balloon and the balloon is in the contracted position. A lubricant is disposed on the outer surface of the balloon at least on a part of the protruding portion of the balloon, and an other portion of the balloon covered by the stent does not have the lubricant.
