Abstract: A transmitter for transmitting an audio signal derived from an audio appliance to an FM (frequency modulation) radio includes a transmitter circuit for converting the audio signal derived from an audio appliance into an FM signal within an FM broadcasting band to thereby transmit the FM signal, a receiver circuit having at least a tuner unit; a display for displaying thereon a frequency; and a control circuit for controlling a transmission frequency of the transmitter circuit and a reception frequency of the receiver circuit. The control circuit causes the receiver circuit to detect an unused frequency within the FM broadcasting band and to set a frequency corresponding to the detected unused frequency to the transmission frequency, and also causes the display to display thereon the set transmission frequency.