The transmission rate of RDS data is 1.1875kbit/sec, and RDS data are encoded by differential encoding method. Then the encoded RDS data are modulated by BPSK using a clock of 1.1875kHz. The modulated RDS data is are modulated by carrier suppressed amplitude modulation using a subcarrier of 57kHz. And that signal are multiplexed into an FM radio wave. RDS data are obtained by demodulating the received RDS modulation signal in RDS demodulator. First, the RDS modulation signal is extracted from an FM radio wave using a band pass filter. The BPSK signal is obtained from extracted RDS modulation signal by a 57kHz carrier recovery circuit. Then the bit rate clock of RDS data is extracted from the BPSK signal, and the BPSK signal is demodulated using the extracted clock signal. Then the RDS data are decoded by a differential decoding method using the demodulated BPSK signal.