| 摘要 |
PROBLEM TO BE SOLVED: To obtain a high-accuracy value by measuring the prescribed signal characteristics relating to the recording data readed out by a data reading out means, determining sample information in correspondence to a focus bias and setting the focus bias regarded optimum by the determined sample information. SOLUTION: The output of a differential amplifier 42 is subjected to phase compensation in a phase compensation circuit 43 and is supplied as a focus coil drive signal FDR to a focus coil driver 16a. The focus coil of a biaxial mechanism is driven by the focus coil driver 16a according to the focus coil drive signal FDR inputted therefrom, by which an objective lens is moved in a direction where the focus coil attaches and detaches to and from a disk. If the focus offset value to be outputted in a target value control circuit 41 is zero, a focus servo loop circuit system is driven by controlling a focus error signal level so as to be made zero.
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