PURPOSE: To prevent external disturbance such as noise from being transmitted to a control circuit, by providing a parallel circuit connected/disconnected with on/off of each analog switch and extracting an impedance output from both ends of the parallel circuit.

CONSTITUTION: A voltage between connecting terminals 42, 43 is changed via remote control lines 40, 41 attended with the change in the resulting resistance of a variable resistor circuit 59 depending of the selected position of a temperature set switch 58. This voltage is applied to non-inverting inputs A2∼A4 of operational amplifiers OP2∼OP4 of a temperature set circuit 60 and compared respectively with a reference voltage of connecting points 65∼67. Further, the amplifiers OP2∼OP4 and analog switches AS1∼AS3 are operated and plural kinds of impedance signals are transmitted from set signal lines 73, 74 connected across the parallel circuit 72 to a burning control circuit 75. Even if the remote control wires 40, 41 are made long, there is no care about the transmission of external disturbance such as noise invaded to the lines 40, 41 into the circuit 75 directly through the constitution above.