Patent ID: 7339872

Claim:
An optical disc device comprising: a mark width identifying flag generation unit for generating a detection flag at a time when a predetermined mark width is detected in an optical reproduction signal that is reproduced from an optical recording medium on which data are digitally recorded according to a pattern of recording code in which probabilities of occurrence of marks and spaces are almost the same; a distortion factor measuring unit for measuring a factor of a mark distortion in a waveform occurring due to an imperfect mark shape, at a position identified by the detection flag that is outputted from the mark width identifying flag generation unit; and a partial response maximum likelihood (hereinafter, referred to as PRML) signal processing unit that is realized by a combination of a partial response equalization unit for performing a partial response equalization to the optical reproduction signal with reference to an intentional waveform interference that can reduce high frequency components which are included in the optical reproduction signal, and a maximum likelihood decoding unit for estimating a most likely sequence, said optical disc device setting a maximum likelihood decoding threshold level for estimating a sequence in the maximum likelihood decoding unit according to the mark distortion factor, at a level at which demodulation data are not erroneously demodulated, with respect to a sequence that is judged by the mark width identifying flag generation unit as a long mark pattern.