Patent ID: 8049986

Claim:
A magnetic disk device including: a magnetic disk possessing a track in which a plurality of magnetic elements magnetically separated from each other are arranged in a predetermined array period; a magnetic head which follows the track and writes data upon receiving a recording signal possessing a time period corresponding to an array period of the plurality of magnetic elements; and a control circuit configured to perform a control method, the control method comprising: writing the data by varying a phase of the array period of the plurality of magnetic elements or a phase of the time period of the recording signal in one section of the track from a corresponding phase in another section of the track; reading a reproduction signal from the track; and determining a phase shift between the array period of the plurality of magnetic elements and the time period of the recording signal, based on a reproduction signal read from the one section and a reproduction signal read from the other section, wherein the determining the phase shift between the array period of the plurality of magnetic elements and the time period of the recording signal is performed, based on a magnitude of a relation between the amplitude of the reproduction signal read from the one section and the amplitude of the reproduction signal read from the other section.