PURPOSE: To supply constantly proper heating capacity with respect to thickness of food by a method wherein a lower surface temperature and a lower surface temperature variation ratio are outputted, a fuzzy deduction is made based on control rules taken out of respective memories, and operation volumes of an upper surface heater and a lower surface heater are obtained.

CONSTITUTION: A lower surface temperature is detected from an output of a lower surface temperature sensor 24 which is in contact with a lower surface of a food which is spaced by a prescribed distance from a lower surface heater 26b, a lower surface temperature variation ratio at a time of continuous power supply to an upper surface heater 26a is detected, and an operation is made based on control rules taken out of a first memory 32 to determine a thickness of the food. Next, from a determination result of the thickness of the food, an operation is made based on control rules taken out of a second memory 34 to determine operation volumes of the upper surface heater 26a and the lower surface heater 26b at a time of heating start. From the outputs of an upper surface temperature detecting means 28 and a lower surface temperature variation ratio output means 29, an operation is made based on control rules taken out of a third memory 36 to determine operation volumes of the upper surface heater 26a and the lower surface heater 26b after heating started.