An object of the present invention is to provide a balloon catheter with whichrupture of a balloon due to forced feeding of a liquid into the balloon havinganextended shape, and treatment with a balloon having a shape that is notsuitable forthe treatment, can be prevented. The present invention provides a ballooncathetercomprising: an inner cylinder shaft having a small-diameter inner cylindersection inthe tip side and a large-diameter inner cylinder section in the base-end side；an outercylinder shaft in which the inner cylinder shaft is inserted in its lumen； aballoonwhose tip is fixed at the tip of the inner cylinder shaft, and whose base endis fixed atthe tip of the outer cylinder shaft, wherein the outer cylinder shaft and theinnercylinder shaft slide over each other to cause a shape change between a normalballoon shape and an extended balloon shape； and a housing which communicateswith the lumen of the outer cylinder shaft, and has a small-diameter lumen inthe tipside and a large-diameter lumen in the base-end side； wherein, by insertingthe large-diameterinner cylinder section of the inner cylinder shaft into the small-diameterlumen of the housing when the balloon has the extended balloon shape,insertion ofthe liquid into the balloon is blocked.
