| 摘要 |
PROBLEM TO BE SOLVED: To highly precisely obtain optimum focus bias for every loaded disk independently of secular change of an optical system and dispersion of conditions due to dispersion for every disk. SOLUTION: On the assumption that a device corresponds to an optical recording medium having an emboss-pit region L1 and an over-write region L2, reproduction is performed varying focus bias for the emboss-pit region L1, and first focus bias being optimum by corresponding to the emboss-pit region L1 is obtained based on a jitter value obtained at this time. Second focus bias being optimum by corresponding to the over-write region L2 is obtained by giving offset quantity obtained by a previous measured result to the first focus bias.
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