Provided is a balloon catheter having a reduced diameter and improved insertion characteristics. This balloon catheter 10 has an inner tube 20 having a main lumen 21 and also has an outer tube 30 for forming an expansion lumen 31. A part of the inner tube 20 is connected to the outer tube 30 at a position closer to the proximal end than a balloon 40, a side hole 45, through which the main lumen 21 is open to the outside, is provided at the connection section, and a weak section 28 is provided to the inner tube 20 at a position closer to the distal end than the side hole 45, the weak section 28 having lower rigidity than the remaining portion of the inner tube 20, the weak section 28 being configured so that, when the balloon 40 is expanded by fluid supplied to the expansion lumen 31, the weak section 28 is pressed by the fluid pressure to close the main lumen 21 of the inner tube 20.
