In the start up of the magnetic disk apparatus, the phase relation between servo information numbers recorded on the magnetic disk 15 in advance and the eccentricity of the magnetic disk is learned. In the positioning of the magnetic head, a signal generated by multiplying, by a weight coefficient, a sine wave or a cosine wave the phase the revolution frequency of the magnetic disk is fed forward as an eccentricity control amount, whereby the eccentricity is compensated.

 
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