A radiofrequency thermal balloon catheter uniformly heats tissues in contact with the balloon to achieve thermotherapy such as ablation or hyperthermia safely and properly for a diseased part. The radiofrequency thermal balloon catheter includes a catheter (4) having an outer shaft (2) and an inner shaft 3 extended through the outer shaft so as to be slidable relative to the outer shaft, an inflatable balloon (6) capable of being inflated so as to be in contact with a target lesion (18) and provided between respective front end parts of the outer and the inner shaft, and a radiofrequency electrode (8) extended in a wall of the balloon or inside the balloon to be used for radiofrequency energy supply in combination with a counter electrode (53). The counter electrode is disposed at a predetermined position, for example, inside the balloon, in the wall of the balloon, in a position neighboring the balloon or on the patient's body surface. A lead wire (10) electrically connects to the radiofrequency electrode. A temperature sensor (12) is capable of sensing temperature of a liquid contained in the balloon. A temperature distribution uniformizing device (14) uniformizes the temperature distribution in the liquid contained in the balloon.