A disturbance compensation signal is produced by estimating the magnitude of
disturbance
acting upon an actuator based on a driving signal and a voltage signal generated
when driving the actuator. A control signal is produced by multiplying the disturbance
compensation signal by a gain adjustment coefficient. A head position error signal
is produced based on the target position of a magnetic head and the current position
of the magnetic head that is detected based on servo information recorded in advance
on a magnetic disk. A gain adjuster obtains the driving signal by adding together
the control signal and a position control signal. The actuator is driven with the
driving signal output from the gain adjuster.
