PURPOSE: To improve productivity and quality by providing a subtraction means which subtracts the number of tracks shifted from the number of a track on which a positioning control means positions a magnetic head and reports the effect to a host device.

CONSTITUTION: When the host device 2 wants the number of the track where the magnetic head at that time is positioned, a microprocessor circuit 4 returns the value obtained by subtracting the value of a track shift designation switch 8 from the number of the track on which actually magnetic head is positioned to the host device 2 through an interface logic circuit 3. Accordingly, the host device 2 does not sense that the number of the track propagate through the interface logic circuit 3 has a deviation from the track number which the track actually seeks. Thus such adjustment can be made that defects of a magnetic disk medium never comes to a specific track which ensures no defect and is seeked according to the instruction of the host device, and therefore the manufacturing yield of a magnetic disk device can be improved.