A radio-frequency thermal balloon catheter is capable of reducing an upper-lower temperature difference in a balloon due to convection to naught and of uniformly heating tissues in contact with the balloon at an optimum temperature to achieve the safe thermal treatment of a lesion. The radio-frequency thermal balloon catheter includes a catheter tube (3) including an outer tube (1) and an inner tube (2), a balloon (4) connected to an end part of the outer tube and an end part of the inner tube, and capable of coming into contact with a target diseased part (41) when inflated, a radio-frequency electrode (6) placed in the wall of the balloon or inside the balloon to transmit radio-frequency current, a lead wire (7) electrically connected to the radio-frequency electrode, a temperature sensor (8) capable of measuring temperature inside the balloon, and a swirling current producing means (12, 16, 20) for making a fluid contained in the balloon swirl in a vertical plane in the balloon so as to reduce an upper-lower temperature difference between an upper part and a lower part of the interior of the balloon due to convection of the fluid to naught.