PURPOSE: To prevent partial extraordinary heating and to carry out thawing uniformly in a short time, by controlling the oscillation output of a high-frequency oscillating part corresponding to the strength of leakage electrical radiation generated from heating electrodes for dielectric heating during thawing.

CONSTITUTION: Direct electric power obtained from a low-frequency alternating source through the electric source part 7 is applied to the high-frequency oscillating part 8, the direct electric power is converted to high-frequency power by the high-frequency oscillating part 8, and applied to the space between the heating electrodes 2 and 3, so that the material 4 to be thawed is heated. Since a high-frequency voltage is applied to the space between the heating electrodes 2 and 3 during thawing, the high-frequency output is partially leaked as electrical radiation. This leakage electrical radiation is collected by the pickup coil 9, and it as electric current is sent to the control part 10. Fluctuations in high- frequency output can be detected as fluctuations in electric current flowing in the pickup coil 9. The control part 10 acts in such a way that the high-frequency oscillating part 8 is regulated in order to suppress the flucutations in electric current.