Servo control apparatus for controlling position of device

A position control apparatus comprising:

• a reading device for reading information from a track formed on a recording medium shaped in a disk by irradiating a light beam to said track, said reading device outputting said read information as an information signal;
• a first detecting means for detecting a quantity of a shift between a position of an irradiation of said light beam and a position of said track on the basis of said outputted information signal and generating a shift quantity signal corresponding to said detected quantity of the shift;
• a sampling means for sampling a low frequency component from said generated shift quantity signal;
• a calculating means for calculating an average of an amplitude of said sampled low frequency component during a period of one rotation or N (N is a natural number) rotations of said recording medium;
• a comparing means for comparing said calculated average with a predetermined value and generating a drive timing signal corresponding to a difference between said calculated average and said predetermined value;
• a generating means for generating a drive control signal to be used for controlling a movement of said reading device on the basis of said generated drive timing signal;
• and
• a first driving device for moving said reading device in a radial direction of said recording medium on the basis of said generated drive control signal.