PURPOSE: To make it possible to perform highly stabilized temperature control, by utilizing functional relationship of the temperature and the resistance value of a temperature sensitive element, and making it possible to perform control and detection by one element.

CONSTITUTION: When the value of an arbitrary temperature is set by an input part 5, the resistance value corresponding to the temperature value is computed by a function operator 6. Said resistance value and the actual resistance value of a thermistor 4 are inputted to a differential operator 7. A current is supplied to a Peltier element 3 through a control circuit 8 so that the difference between said resistance values becomes zero. The actual resistance value of the thermistor 4 is obtained by a constant current circuit 9 and an A/D converter 10, which converts the voltage output of the circuit 9 into a digital quantity. A feedback loop of l4→9→10→7→8→4 is operated until the balance to the preset temperature is obtained. The resistance value of the thermistor 4 ( the output of the A/D converter 10) is directly converted into the temperature by a function operator 11. Thus the highly stabilized temperature control can be performed.