PURPOSE: To prevent a thermo module from being destroyed due to temperature by continuing the disconnection state of power supply when thermoelectric power is excessive.

CONSTITUTION: This circuit is provided with a switch circuit 3 performing the connection or disconnection between a power source 1 and a thermo module 2, a switching element 4 performing the switching control of the switch circuit 3 and an oscillation circuit 7 performing the turning on and off control of the switching element 4. The switch circuit 3 is switched by the output of the switching element 4 and the switching element 4 is controlled by the output of the oscillation circuit 7. When the output of the oscillation circuit 7 is on a high level, the switching element 4 is turned on and the switch circuit 3 disconnects between the power source 1 and the thermo module 2, and when the switching element 4 is turned off, the switch circuit 3 connects between the power source 1 and the thermo module 2.