PURPOSE: To accurately detect an end of cooking time by correcting a deviation of an initial value of an optical sensor for sensing a generating amount of substance for shutting OFF a light such as smoke, etc., to be generated in a cooking chamber.

CONSTITUTION: A relay RL3 is turned ON at the initial time of starting to heat to cook thereby to drive a blower motor BM, thereby discharging smoke generated upon scorching of oil, etc., at the time of previous cooking out of a cooking chamber. Input of a detected value from an optical sensor 7 to a smoke sensor 12 is stopped during this period. When a predetermined time is elapsed and the discharge of the smoke is finished, the motor BM is stopped, and the detected value from the sensor 7 is stored as an initial value in a memory of a controller 10. A deviation from the detected value from the sensor 7 thereafter is sequentially obtained. When the deviation reaches a set value, a relay RL4 is turned OFF to stop heaters 3, 4 thereby to finish heating to cook.