[Problem] An object of the present invention is to provide a high frequency cancer thermotherapy apparatus capable of improving therapeutic effects and reducing burdens on a patient. [Means for solving the problem] A high frequency cancer thermotherapy apparatus that treats by generating a high frequency electric field between apairof electrode parts which sandwich a patient and are disposed so as to be opposite to each other and performing a dielectric heating with respect to an affected part, comprising: a bed for thermotherapy that comprises a bed part and a bed supporting part for liftably/lowerably and horizontally movably supporting the bed part； a gantry on which the electrode parts are mounted； and a high frequency generation and control part, wherein a maximum-sized electrode part which can be mounted on the gantry is an electrode part comprising an electrode plate having a size that a diameter size exceeds 300mm and a pad attached on the electrode plate, wherein the bed part comprises an opening part which is formed to a size that the maximum-sized electrode part can pass from a vertical direction； a shutter which opens/closes the opening part； and a bed surface flatization means which comprises slide type tables for flatizing a level difference in a bed surface of the bed part which occurs in a state of closing the opening part by the shutter.
