An information record and playback apparatus configured to perform record and playback operations of an optical disk which is provided with data recording tracks having a surface wobbled at a predetermined frequency and a plurality of prepits formed with a predetermined phase relation to the position for data recording. The apparatus includes at least a demodulation circuit which operates for a predetermined error flag be indicated at the position of the assumed LPP data bit, when the error pattern is detected to be other than ‘1’ or ‘0’, that may be caused, for example, by noise. Erasure correction with the Reed-Solomon code therefore becomes feasible using the error flag. This achieves error correction of a number of errors even using fewer added data, thereby offering advantages in increasing efficiency in the error correction.