An interface device includes: at least one configuration channel terminal for communicating configuration information, wherein whether the interface device itself is in connection and whether the interface device itself is at a high voltage side or a low voltage side are determined according to a voltage or current status at the configuration channel terminal; a multi-functional transmission line, which includes a thermistor; and a temperature monitor circuit, coupled to the multi-functional transmission line, for sensing a temperature status to generate a temperature sensing signal. When two interface devices are connected with each other, the thermistor and the temperature monitor circuit can be located together in one of the interface devices or separately located in different interface devices.