In order to reproduce data in a stable manner by correction of random and burst errors of a wide range without lowering a transfer speed, C2 error correction for correcting an inter-sector error is carried out in addition to the conventional C1 error correction for correcting an error generated in a sector. The configuration of an error correction unit (or an ECC block) including C1 and C2 codes is formed as a track. That is to say, one track is used as the base of an ECC block unit. In this way, two ECC block units never exist in the same track.