An acoustic signal transmission method comprising: a selection step, in a transmission source, of selecting a carrier frequency of a data signal and a PN sequence corresponding to the carrier frequency; a modulation step, in the transmission source, of modulating the carrier frequency selected by the selection step by using the data signal; a generation step, in the transmission source, of generating a symbol synchronization signal according to the PN sequence selected by the selecting step; a superposition step, in the transmission source, of superposing the symbol synchronization signal generated by the generation step and the data signal modulated by the modulation step onto the acoustic signal and transmitting thus obtained signal; a reception step, in a transmission destination, of receiving the acoustic signal superposed with the modulated data signal; a calculation step, in the transmission destination, of calculating correlations between the acoustic signal received by the reception step and a plurality of PN sequences; a determination step, in the transmission destination, of determining the PN sequence having the highest maximum correlation value with the received acoustic signal in the plurality of PN sequences according to a result of calculation by the calculation step; a synchronization processing step, in the transmission destination, of deciding a synchronization point by using the PN sequence determined by the determination step and performing a symbol synchronization process of the modulated data signal superposed on the acoustic signal according to the synchronization point; and a demodulation step, in the transmission destination, of demodulating the modulated data signal subjected to the synchronization process by the synchronization processing step. a selection step, in a transmission source, of selecting a carrier frequency of a data signal and a PN sequence corresponding to the carrier frequency; a modulation step, in the transmission source, of modulating the carrier frequency selected by the selection step by using the data signal; a generation step, in the transmission source, of generating a symbol synchronization signal according to the PN sequence selected by the selecting step; a superposition step, in the transmission source, of superposing the symbol synchronization signal generated by the generation step and the data signal modulated by the modulation step onto the acoustic signal and transmitting thus obtained signal; a reception step, in a transmission destination, of receiving the acoustic signal superposed with the modulated data signal; a calculation step, in the transmission destination, of calculating correlations between the acoustic signal received by the reception step and a plurality of PN sequences; a determination step, in the transmission destination, of determining the PN sequence having the highest maximum correlation value with the received acoustic signal in the plurality of PN sequences according to a result of calculation by the calculation step; a synchronization processing step, in the transmission destination, of deciding a synchronization point by using the PN sequence determined by the determination step and performing a symbol synchronization process of the modulated data signal superposed on the acoustic signal according to the synchronization point; and a demodulation step, in the transmission destination, of demodulating the modulated data signal subjected to the synchronization process by the synchronization processing step.