According to one embodiment, a magnetic disk device includes a magnetic disk, a storage unit, a magnetic head, an error correction unit that, in a case where an error is detected in user data read by the magnetic head, performs error correction on a sector in which the error is detected in track units and acquires error correction data, and a control unit. The control unit controls reading/writing of user data, management data for managing a sector on which the error correction is performed in the track units, and the error correction data, and in a case where there is no host access, rewrites data on the track including the sector on which the error correction is performed, based on the user data stored in the track and the error correction data of the sector, in which the error is detected, of the track.