An equalizer (22) performs a PR equalization of a reproduced signal waveform output from an A/D converter (21). A reference-waveform generation unit (42) generates a reference reproduced-waveform based on a recording data train estimated from the reproduced signal waveform by a recognition unit (30). An equalization-error calculation unit (43) calculates an equalization error between the reference reproduced-waveform and the reproduced signal waveform. A transient equalization-error detector (44) extracts equalization error information, as a transient equalization error, at the time instant at which the reference reproduced-waveform assumes a specific level, and at which the specific level-value and a level-value of the reference reproduced-waveform at one channel clock before or after the time instant satisfy therebetween a specific relative relationship. The extracted transient equalization error is used as an index showing the quality of the recorded mark.
OPTICAL INFORMATION RECORDING/REPRODUCING UNIT AND METHOD OF MEASURING RECORDED-MARK QUALITY