A transmitter-receiver comprises a transmitter, a transmitter circuit, a receiver circuit, a receiver, a jack, and a switch. The transmitter circuit converts a first audio signal to a transmit signal and transmits the transmit signal. The receiver circuit extracts a second audio signal from a received signal. The jack is adapted to be connected with a plug of an external transmitter-receiver. The switch is on/off controlled dependent on whether or not the jack of the external transmitter-receiver is connected with the plug. The switch, when the jack is not connected with the plug, supplies the first audio signal from the transmitter to the transmitter circuit and also supplies the second audio signal from the receiver circuit selectively to the receiver. Further, the switch, when the jack is connected with the plug, supplies an input signal from the external transmitter-receiver to the transmitter circuit through the connected plug and jack and also supplies the second audio signal from the receiver circuit selectively to the external transmitter-receiver through the connected jack and plug.