PURPOSE: To require only one burn-out detecting circuit and to execute highly accurate thermocouple signal measurement by connecting the burn-out detecting circuit to the output side of a thermocouple signal selecting switch.

CONSTITUTION: Since the burn-out detecting circuit B1 is connected to the output side O1 of the thermocouple signal selecting switch 1 to which plural thermocouples T1 to Tn corresponding to n channels are connected, the existence of burn-out (disconnected state) in each channel switched by an external signal 3a is eletected by the common burn-out detecting circuit B1 connected on the output side. On the output side, output data 4a in a thermocouple signal measuring mode are A/D converted by an A/D converter 5 through an amplifier 4 and inputted to a computer 3 as converted data. Since respective channels are mutually insulated, noise inserted into one channel does not exert adverse influence to other channels.