a large external force is acting on the control target fig3 is a graph view experimental result showing control command in performing the seek to the direction that the external force is large the horizontal axis of the graph view shown in fig3 represents time millisecond and the vertical axis represents control command value provided to the d a converter 19 from magnitude a of the control command value at the seek end it can be seen that the external force of about 10 of the maximum control command value is working in the magnetic disk apparatus used in this experiment as shown in fig3 it can be seen that in the seek to the direction that the external force such as magnet latch force is large the transient response does not occur because the control system of the embodiment does not require switching of the control structure furthermore as described later also in the seek to the direction that the external force is small discontinuous control command does not occur because switching of the control structure is not required as described above the output of the phase lead compensator 120 is input to the model side control system 200 through the gain vector 150 and the output of the integrator 110 is input to the actuator vcm 13 through.