An object of the present invention is to provide a balloon catheter with which rupture of a balloon due to forced feeding of a liquid into the balloon having an extended shape, and treatment with a balloon having a shape that is not suitable for the treatment, can be prevented. The present invention provides a balloon catheter comprising: an inner cylinder shaft having a small-diameter inner cylinder section in the tip side and a large-diameter inner cylinder section in the base-end side； an outer cylinder shaft in which the inner cylinder shaft is inserted in its lumen； a balloon whose tip is fixed at the 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 to cause a shape change between a normal balloon shape and an extended balloon shape； and a housing which communicates with the lumen of the outer cylinder shaft, and has a small-diameter lumen in the tip side and a large-diameter lumen in the base-end side； wherein, by inserting the large-diameter inner cylinder section of the inner cylinder shaft into the small-diameter lumen of the housing when the balloon has the extended balloon shape, insertion of the liquid into the balloon is blocked.
