PURPOSE: To improve a reliability on a heating action of a temperature control, by a method wherein an internal temperature or an average temperature of an object to be heated is easily and reliably detected from a spit supportably transfixing the object to be heated in a heating chamber.

CONSTITUTION: A spit 10, suportably transfixing an object to be heated, for example, a lump of meat, is hollow and made of a metal having improved thermal conduction, and a temperature-sensitive element, for example, thermistor is placed at an approximately central inside in the axial direction. The object to be heated is heated with high frequency from a heater 6 and a magnetron 8, and the heat of the object to be heated is transferred to the thermistor through the spit 10. A temperature adjustor actuates through the output of the thermister.