A spread spectrum communication system includes a transmitter having: a data generator for generating a data signal; a pn generator for generating a first pn signal in accordance with a pn code clock; a modulator for modulating the pn code clock by synchronizing the data signal with a multiple N of one period of the first pn signal; a first part for detecting one period of the first pn signal; a second part for outputting a clock to the data generator in accordance with a converted period equal to a multiple N of the detected period; and an output part for transmitting a signal at an output of the pn generator, and a receiver which receives the transmitted signal, the receiver having: a second pn generator for generating a second pn signal in synchronism with the transmitted signal; a demodulator for demodulating the transmitted signal with the second pn signal; a third part for detecting one period of the second pn signal; a fourth part for outputting a timing signal in accordance with a converted period equal to a multiple N of the detected period; and a discriminator for detecting each bit of a demodulated signal in synchronism with the timing signal.