To shorten burnout detection time, even when constituting a temperature detecting system by connecting two or more of burnout detection circuits to one thermocouple.

The burnout detecting circuit is constituted so that the temperature is measured based on electromotive force generated when detecting the temperature of a temperature sensor 11 of the thermocouple, and a bias current capable of controlling supply/non-supply is supplied to its temperature sensor 11, and in this supply, when voltage charged to a first capacitor 27 via a first resistor 26 exceeds a predetermined threshold, it is detected as disconnection of the temperature sensor, and has a second capacitor 62 connected via a second resistor 61 and having capacitance sufficiently smaller than the first capacitor 26, and a comparing means 64 to output a burnout detecting signal when the applied voltage exceeds reference voltage by applying a voltage by charging to the second capacitor 62 by the bias current on a voltage comparing end, between a supply point of the bias current and the earth.