A diffusion code generating method for a code division multiplex communication by a spread spectrum system is provided. A receiving apparatus according to the above method receives the signal which was multiplexed by using a plurality of sets of diffusion codes and comprises: a generator to generate a sync code and a plurality of sets of diffusion codes other than the sync code; a correlator to obtain a correlation between a reception signal and the sync code generated from the generator; and a receiver to receive the reception signal on the basis of the plurality of sets of diffusion codes generated from the generator. The generator generates the sync code in a manner such that the cross-correlation values are set to very small values at positions near a code sync point or are enough smaller than the autocorrelation peak of the sync code or are set to very small values at both of or either one of the positions before and after the code sync point.