PURPOSE: To provide a proper heating output regardless of power source voltage fluctuation by detecting power source voltage, and increasingly and decreasingly correct microwave heating output according to this.

CONSTITUTION: When control is started, the value of the present power source voltage V is judged on the basis of the output of a power source voltage detecting circuit 38. To basic heating patterns, wattage correction corresponding to voltage fluctuation is conducted every pattern, and this value is set as the actual magnetron output. A magnetron 13 is ON, and for the oven thawing heating of a material 40 to be heated at the set output, the magnetron 12 is ON/OFF in the above pattern, considering voltage fluctuation to conduct the duty control of the output. When the full set cooking time is elapsed, completion of cooking is judged by a humidity sensor 15 on the basis of this, and the magnetron 13, a turn table 14, and a fan motor 12 are OFF to complete the thawing cooking control.