According to one embodiment, there is provided a magnetic disk device including a magnetic disk, a magnetic head, and a controller. The magnetic head is opposite the magnetic disk. The magnetic head includes a first read head and a second read head. The controller determines a track pitch in the vicinity of a first track or a second track adjacent to the first track of the magnetic disk based on first position information and second position information. The first position information depends on a servo signal read by the first read head and corresponds to the first track. The second position information depends on a servo signal read by the second read head and corresponds to the second track.