A decoder for spectrum diffusion signals is capable of reproducing data from received a spectrum diffusion signal, such as satellite communication signals, without performing PN synchronization. The decoder comprises a correlation detector comprising a matched filter which produces a back-diffusion signal when a received spectrum diffusion signal correlates with a Gold code for a specific channel of a station, an extraction signal generator for detecting the epoch position of a peak of a triangular wave which appears in the output of the correlation detector and providing an extraction signal when correlation between the spectrum diffusion signal and the specific Gold code identifying the corresponding channel is established, and a data output extractor responsive to the extraction signal to extract the back-diffusion signal from the output of the correlation detector and reproduce the resulting data. In this arrangement, the extraction signal generator is responsive to the peak of the triangular-form wave in the back-diffusion signal from the correlation detector to output the extraction signal. Therefore, according to the invention, it is unnecessary to perform PN synchronization in order to obtain data from the spectrum diffusion signal.