An object of the present invention is to provide an oblique inflation type balloon catheter in which a balloon may be obliquely inflated to tilt with respect to a main body tube without a central axis of a blood vessel being shifted from a central axis of a catheter body even when the blood vessel is curved, and rarely slips without a contact area with respect to the blood vessel decreasing and a wrinkle being formed on the balloon in a deflated state, and which may increase a degree of adhesion between a blood vessel wall and the balloon to prevent blood leakage, and a balloon base. The balloon catheter of the present invention is provided with a balloon base (5) at a front end of a tubular catheter body (2) having a predetermined length. The balloon base (5) includes a cylindrical base (15) having a larger diameter than an outer diameter of the catheter body, and a lumen (6) having substantially the same diameter as the outer diameter of the catheter body is formed on the base over an entire length with both ends opened. A central axis of the lumen is inclined at a predetermined angle with respect to a central axis of the base concentric with a central axis of the catheter body, and an outer peripheral surface is formed in parallel with the central axis of the base. The balloon (3) is provided on the outer peripheral surface of the parallel base to obliquely inflate with respect to the central axis of the catheter body (2) during inflation.
