A transmitter and receiver circuit includes antennas for receiving high-frequency signals; a local oscillator for generating local oscillation signals; mixers connected to respective antennas for converting the frequency of the high-frequency signals from corresponding antennas in response to the high-frequency signals input from the local oscillator; and a switch for inputting the local oscillation signals generated by the local oscillator into a selected one of the mixers so that receiving channels are switched by the switch.