To attain improvement in reliability, even in the case of a still image by temporarily stopping detection due to a first detecting means when a second detecting means detects that first data are not changed, and restarting the temporarily stopped detection due to the first detecting means, when the second detecting means detects that the first data are changed.

Regenerative data are sent from a pickup 10, which reads out a signal on a disk 11, to an extension and demodulation processor 13. At the extension and demodulation processor 13, the data are demodulated and extended corresponding to a modulation system. A detector 14 for embedded data detects transmission data as many as the number of repetition from pixel blocks, in which the transmission data are embedded. A majority decision device 15 makes a majority decision for each bit for the transmission data detected as many as the number of repetition and composes the transmission data of majority data. An error corrector 16 detects and corrects an error corresponding to an error-correcting code in the transmission data.