PURPOSE: To make it possible to detect correct humidity and control accurate heating, by installing an air suction port and an exhaust air port in a heating chamber, and a humidity sensor in parts where the wind in the exhaust duct is concentrated.

CONSTITUTION: The wind supplied into a heating chamber 2 from an air suction port 9 directly drops toward food 20 as it is. As a result, an environment which includes water vapor generated from the food 20 during heating move with the wind almost altogether. Then, the wind with the environment is collided with the four side walls of the heating chamber 2, and rises along the walls. Then, they are discharged efficiently from a plurality of exhaust air ports 14 provided on an upper wall 10. The wind and environment discharged outside the heating chamber in this manner are concentrated near a humidity sensor 18 inside an exhaust air duct 15. It is, therefore, possible to detect accurately the humidity in the heating chamber 2 based on the water vapor included in the environment discharged efficiently outside the heating chamber.