To provide the signal compression method of high compression efficiency by detecting the phase difference of the signals of plural channels, adjusting the phase of the signals based on the phase difference and delay quantity calculated from the phase difference and obtaining a difference signal.

When signals s1 and s2 are inputted to channels L and R respectively, they are one stored in RAM memories 13 and 23 respectively. The phase difference of both signals by mutual correlation is extracted from the memoirs 13 and 23 by a phase difference extraction device 31. A delay quantity calculation device 32 calculates the phase difference as delay quantity. The delay quantity and which signal advances as the signal are stored in a parameter memory 33. An instruction is given to a delay device 14 or a delay device 24 and the advanced signal is delayed by the delay quantity. Thus shift quantity on a time axis is dissolved and it can be taken out as a difference. Then, a differential waveform can sufficiently be reduced.