The purpose of this invention is to provide a balloon catheter whereby rupture of the balloon due to liquid being forced into the balloon with the balloon extended or treatment with a balloon shape that is unsuitable for treatment can be prevented. This invention provides a balloon catheter that comprises the following: an inside tube shaft that has a narrow inside tube section at the distal end and a wide inside tube section at the proximal end an outside tube shaft with the inside tube shaft inserted into the lumen thereof a balloon the distal end of which is affixed to the distal end of the inside tube shaft and the proximal end of which is affixed to the distal end of the outside tube shaft that changes between a normal shape and an extended shape as a result of the outside tube shaft and the inside tube shaft sliding against each other and a housing that connects to the lumen of the outside tube shaft and has a narrow lumen at the distal end and a wide lumen at the proximal end. When the balloon is extended the wide inside tube section of the inside tube shaft is inserted into the narrow lumen of the housing blocking the insertion of liquid into the balloon.
