PURPOSE: To provide a power monitoring device used for various kinds of electric cookers, which can rapidly detect a decrease in a.c. source power.

CONSTITUTION: An input terminal of a voltage comparator 14 for delivering a signal when the input voltage is between first and second threshold values, is connected to a voltage dividing point of a d.c. power source 4 composed of a first resistor and a second resistor. Further, one end of an a.c. power source 10 is connected to the voltage dividing point through a circuit in series of a constant voltage element and a third resistor 3, and the other end of the source 10 is connected to a positive terminal of the d.c. power source 4, thereby it is possible to realize the power source monitoring device for an electric cooker which can rapidly detect lowering of the voltage of the a.c. power source 10.