PURPOSE: To always execute a stable demodulation by correct range informtion, by transmitting plural pieces of same range information continuously together with differential encoding signals, and accumulating the differential encoding signals only when the range information has been matched at the time of demodulation.

CONSTITUTION: The 7 bit DPCM signal RD and the 1 bit code signal SI are recorded in the disk at the period of 33μ sec. Also, the range signal of 2 bits AQ is recorded at every 0.1 sec. The PCM signal of 12 bits RS which has been AD-converted is recorded at every 0.1sec or so, and even if an error bit is contained in the DPCM signal RD and the range signal AQ at the time of regeneration, the DPCM→ PCM conversion (demodulation) at the regeneration side can be executed on the basis of the PCM signal RS having a correct level, at all times.