A balloon catheter includes an inner cylinder shaft having a small-diameter inner cylinder section in a tip side and a large-diameter inner cylinder section in a base-end side; an outer cylinder shaft with the inner cylinder shaft in its lumen; a balloon whose tip is fixed at a tip of the inner cylinder shaft, and whose base end is fixed at the tip of the outer cylinder shaft, wherein the outer cylinder shaft and the inner cylinder shaft slide over each other and cause a shape change between a normal balloon shape and an extended balloon shape; and a housing communicating with the lumen of the outer cylinder shaft, and having a small-diameter lumen in the tip side and a large-diameter lumen in the base-end side; wherein the housing has an insertion inlet for insertion of the inner cylinder shaft, and a liquid inlet/outlet.