PURPOSE: To detect accurately a temperature extending over a wide range without being affected by floating volume or frequency characteristics of an oscillation element, by keeping the oscillation frequency of an oscillator constant regardless of temperature fluctuations.

CONSTITUTION: A temperature is detected by an oscillator 10 and an oscillation output fx corresponding to the detected temperature is outputted and then, is compared with a reference frequency fo by a comparator 30. These comparison outputs CM1WCMn are given to an resistance array Rx through a switch control circuit 40 and a switch latch circuit 50 and each resistance element is switched on/off. Further, after detecting coincidence of the output fx and the frequency fo by a coincidence detection circuit 60, a switch Sw is turned off and a thermosensitive resistance variation element Rth is cut off and then, the resistance value of the array Rx is set to the standard resistance value. Then, the control quantity-the correction quantity of the temperature conversion time is found from the oscillation frequency of the oscillator 10 at the standard resistance value and is held. Further, the control quantity is converted into the temperature quantity using the correction quanity as a parameter.