PURPOSE: To provide means for use in sensing a heated state of a food in a heater device of which configuration is simple.

CONSTITUTION: A Piezo-electric element sensor 1 acting as a sensor is arranged at an air discharging part 12 of a micro-wave oven in such a way as the sensor is contacted with a discharged air got from a heating chamber 6. A heating means 5 is controlled by a control device 4 in response to a signal corresponding to the temperature got from the Piezo-electric element sensor 1. Under this configuration, it is possible to make a simple configuration accompanying the sensor due to the fact that the Piezo-electric element sensor 1 is hardly influenced by contamination of the air discharging flow or by the surrounding air temperature.