In a ceiling part of a heating chamber, a sub-cavity is provided in which a steam-heating heater is housed. Steam generated by a steam generating device is heated by the steam-heating heater inside the sub-cavity to be brought into an overheated state, and is then jetted out through upper jet holes provided in the ceiling part of the heating chamber and through side jet holes provided in lower parts of the side walls of the heating chamber at both sides thereof. Food is supported on a rack to be in a state floating above the floor surface of the heating chamber, and, through the side jet holes, steam is jetted toward under the food.