PURPOSE: To provide a heater capable of preventing an over-cooking, easy setting of an additional heating and providing a convenient operation by a method wherein upon completion of an automatic cooking, a cooking time setting means is operated until a specified period of time elapses and then a setting of an additional cooking time for an automatic cooking performed just before it is carried out within a range of a specified period of time.

CONSTITUTION: An automatic cooking is started by pressing a cooking start key 7 after pressing an automatic heating key 2. After this operation, a completion of cooking is determined by using a timer 8 and a sensor 11 and this is informed to a user with an informing part 10. At this time, a control part 1 energizes the timer 8 and then requests an additional heating in an automatic cooking with an informing part 10 until a specified period of time elapses. During this period, a user rotates a rotary encoder 6 and presses a cooking start key 7, thereby the additional heating can be carried out in response to an automatic cooking performed just before it. With such an arrangement, a setting of the additional heating time can be carried out only with the cooking time setting means without selecting any manual key.