PURPOSE: To eliminate an irregularity in a finishing level by storing a deviation of an absolute humidity sensor from a reference value and correcting it based on the deviation at the time of executing a cooking.

CONSTITUTION: An absolute humidity sensor 14 senses steam generated by heating a material 16 to be cooked, and sends a varying voltage amplitude to a microcomputer 11 through a sensor output amplifier 13. Water of the same quantity of each product is heated for the same time, and varying voltage amplitudes V', V", etc., at that time are measured. Further, a ratio of actually measured values V' or V" to a reference value V is calculated by the microcomputer 11, and stored in an EEPROM 12. The case of actual cooking is presumed, the output voltage amplitude of the sensor 14 is read, and corrected by the ratio of the value V' to the value V stored in e EEPROM 12. Thus, the finishing degree of the cooked material can be made uniform.