PURPOSE: To achieve a thawing close to natural mode quickly in a high frequency heater capable of thawing frozen food by controlling high frequency output with a microcomputer to meet a specified relationship for each of five-stage of heating times divided depending on the weight classified by the type of material to be cooked.

CONSTITUTION: Various materials to be cooked are divided into 5 stages corresponding T1WT5 with a total thawing time of T0 and stored in a microcomputer while high frequency outputs P1WP5 for respective stages T1WT5 are computed and controlled to meet a specified relationship. As a result, the material to be cooked is heated by the max. output for only the time T1 at the rising in the thawing to heat only the surface thereof. Then, the output is shifted to 0 for the time T2 to let the surface temperature to penetrate into the material. For the subsequent time T3, the surface and internal temperature are raised by a low output P3. Thereafter, for the time T4, the output is shifted to 0 again to equalize the temperature and finally, for the time T5 it is heated by a relatively high output P5 to finish. Thus, thawing close to the natural mode can be done.