A heating apparatus such as microwave ovens includes a heating chamber having a door, heaters for heating food contained in the heating chamber, a temperature sensor for sensing a temperature in the heating chamber to provide an output in accordance with the sensed temperature, a gas sensor sensing a volume of gas in the heating chamber to provide an output in accordance with the sensed gas volume, and a microcomputer-based control device. The control device sets a reference value in accordance with the output of the temperature sensor, the reference value being for determining the kind of the food. The control device further calculates a change rate of the gas volume on the basis of the output of the gas sensor. The control device then compares the change rate of the gas volume with the reference value to determine the kind of the food contained in the heating chamber.