The output of a first bridge circuit including as one component element a thermistor for detecting the temperature of a pan is compared with a preset value in a first operational amplifier. The first operational amplifier provides a low level output when the detected temperature is below a predetermined temperature. When this low level output is supplied to a second operational amplifier, the output thereof goes to a high level to turn on a transistor so as to energize a relay for passing current to a cooking heater. When a cooking end temperature is reached, the internal resistance of the thermistor is reduced, and as a result the output of the first operational amplifier goes to a high level, causing the output of the second operational amplifier to go to a low level. Thus, a warming heater is energized while the cooking heater is de-energized.