The medical balloon catheter of the present invention comprises a catheter shaft composed of a distal end shaft and a proximal end shaft and a balloon on the distal end of the distal end shaft, wherein the proximal end shaft is composed of a single member and the distal end portion of the proximal end shaft is lower in rigidity than the other parts thereof. The present invention also provides a medical balloon catheter having a structure in which a tube for passing a guidewire inside thereof is arranged so as to pass inside the balloon and the balloon and tube are fused together in the vicinity of the distal end of the catheter, wherein the ratio of the outer diameter of the small-diameter portion on the distal end side of the tube to the outer diameter of the proximal end portion is no less than 0.85.