PURPOSE: To make it possible to heat and finish properly in consideration of the weight of a container to be used by comparing comparison data equivalent to detected weight by a weight sensor with the change in the output of a gas sensor under actual cooking, and compensating execution time for a finishing heating process based on the comparison result.

CONSTITUTION: Unheated food 12 is heated by high frequency when a magnetron 14 starts its operation. Then, the output of a gas sensor 23 judges points of time Ta, and Tb when a peak value Vsmax drops to αVsmax and judges again the lapse of time from the commencement of heating T0 and the points of time Ta and Tb and moves to a finish heating process. In the previous stage, a weight sensor 18 detects the weight of uncooked food 12, and reads compari son data td equivalent to the detected weight from a memory section 25. After check time ta, and tb are judged, the check time ta and tb are immediately compared with the comparison data td. When it is judged as ta<td, the genera tion period of gas is earlier than a maker-assumed time D, which clearly indicates that the net weight of food 12a is smaller than the estimated value (the weight of a container 12b is larger than estimated).