To execute accurate temperature detection at the time of doubling thermocouples in a heat treating unit for performing heat treatment to a semiconductor substrate.

The larger one of the electromotive forces of one doubled thermocouple and the other thermocouple is selected as a temperature detection value. One connecting terminal of each thermocouple is constituted so that a voltage for pull-up can be switched so as to be supplied or grounded by a switch, and normally connected to a ground side. When the difference or rate of the both electromotive forces is monitored, and the value is made large, that is, when one thermocouple is about to be disconnected, and the electromotive force is made low, it is judged that one thermocouple is disconnected, and the switch related with the other thermocouple is switched to the pull-up side. Afterwards, when one thermocouple is disconnected, control is executed to the safe side (so that it can be recognized that the temperature detection value is high).