In a positioning control device based on control of an observer having a disturbance suppression function, a disturbance suppression function according to a head position is added without impairing the control characteristics of the observer. The position control device has an observer having a disturbance suppression function comprising a model of an actuator and a model of disturbance, and a table for storing an estimated gain of the observer according to a position of the head. And an estimated gain is acquired from the table according to the position of the head, and an estimated gain of the observer is changed so as to change the disturbance suppression frequency characteristic. The disturbance suppression characteristic can be optimized according to the position of the head in the radius direction or between disks, and vibration of the head can be prevented even if recording density is increased.