PURPOSE: To obtain a magnetic disk device capable of performing the positioning of a head correctly by following synchronous/asynchronous shaft runout component included in a position error signal representing the positioning error of a magnetic head.

CONSTITUTION: A periodical component that is the synchronous/asynchronous shaft runout component of a rotary driving mechanism 2 included in the position error signal (A-B) generated from servo information read from a magnetic disk 1 by the magnetic heads 3, 4 is estimated by an FFT 18. A second control signal S2 can be generated by inputting an estimated periodical component to an adaptive filter 16 and applying filter processing by a filter coefficient acquired from the position error signal (A-B). Ahead positioning control signal S3 can be generated by performing the feedforward addition of the second control signal S2 on the first control signal S1 of a main control loop, and the magnetic heads 3, 4 are controlled by shifting to the radial direction of the magnetic disk 1 by using the head positioning control signal S3.