The vascular occlusion balloon catheter has a balloon, a main lumen, and a balloon expanding lumen. The balloon catheter has an air discharge passage. The air discharge passage has a distal end opening located at a position distal from the balloon and a proximal end communicating with an inner portion of the balloon. The distal end opening of the air discharge passage is positioned inside a portion disposed proximally from a distal end of the balloon catheter. The air discharge passage communicates with the main lumen at the distal end opening of the air discharge passage. The area of a cross section of the air discharge passage orthogonal to an axial direction of the balloon catheter is set to 200 μm2 to 450 μm2. The length of the air discharge passage is set to 1.0 to 3.0 mm.