A device for radio-frequency hyperthermia having a first electrode adapted to be disposed in a tract organ of a living body. A second electrode is provided which is adapted to be disposed on an outer circumference of the living body such that the second electrode is opposed to the first electrode such that there is generated a spatially inhomogeneous electric field within the living body in cooperation with the first electrode so that a part of the living body near the first electrode may be heated more strongly than a part of the living body near the second electrode. This serves to selectively heat a tumor or malignancy region at the deep inside of the living body by a noninvasive technique.
