| 摘要 |
PURPOSE:To reduce a fall of recording and reproducing characteristics, caused by a focal shift, and to satisfactorily record and reproduce the information by setting a level of an offset signal to a part where the amplitude of a reproducing signal by recording becomes maximum. CONSTITUTION:A level setting control circuit 30 varies stepwise a level of an offset signal 103 at a prescribed time interval by varying stepwise a level setting signal 104, inputs a recording control signal 120 to a recording circuit 20, and recording in which a focal position has been shifted at a prescribed time interval is executed. The level setting control circuit 30 samples a value of a level signal 115 by the same timing as hat which has varied the offset signal at the time of recording, catches a timing by which the value of the level signal 115 becomes maximum, selects a value of the level setting signal 104 at the time of this recording, and supplies it as an optimum set value to a focus offset generating circuit 11 at all times. In this way, even if a shift is generated in a focus error signal 101, a focal position of light beam 3 is set to an optimum state against recording and reproduction.
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