PURPOSE:To sufficiently reduce the steady-state deviation even if a feed device is miniaturized, by constituting a servo system so that a principal eccentric component of a disk included in a control target value is supplied as the servo signal and the servo gain is raised for this eccentric component. CONSTITUTION:A tracking error signal TE is supplied to a feed device 4 through the second transmission element 24, an adder 25, and a phase compensat ing circuit 27 to allow the feed device 4 to respond to a principal tracking error due to eccentricity of the optical disk. A model circuit 26 showing the response characteristic of the feed device 4 is provided for the purpose of faith fully responding to the extent of eccentricity to eliminate an unstable operation due to friction. The second transmission element 24 is provided which can give a servo gain, which is ideally infinite for the eccentric component, to the feed device 4 having a large mass. Thus, the steady-state deviation in this servo system is very much reduced, and the power consumption is reduced because the servo band of the feed system is narrowed.
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