A head position control system control the position of the head by correcting the components synchronizing rotation of the disk from the head control amount, in which an adjusted gain to minimize the components synchronizing rotation after correction is theoretically acquired. An adjusted gain based on the ratio of the magnitude between the components synchronizing rotation of a disk and the components not synchronizing rotation of the disk in the position signals is used. And a gain to minimize RRO after correction can be theoretically determined using an expression to determine RRO after correction. The gain can be determined without depending on experiment, and the value of RRO after correction can be guaranteed, therefore the manufacturing time and the device specifications can be determined.