In a demodulator for use in the Radio Data System (RDS) as defined by the European Broadcasting Union, transmission of these signals is carried out through phase shift modulation of a suppressed subcarrier, a multiplex signal, which contains a signal with the frequency of the subcarrier passes through a band-pass filter and an amplitude limiter, and the amplitude-limited signal, having a carrier frequency, is sampled at a sampling frequency that is a multiple of the frequency of the subcarrier. The sampling values are summed over a preset portion of one period of the subcarrier. The summed sampling values are supplied to a digital signal processing circuit.