According to one embodiment, a magnetic disk device including a disk, a head that writes data with respect to the disk and reads data from the disk, and a controller that overwrites a second track on a first track in a radial direction of the disk, performs first alternative processing of recording a first user sector in a first region when writing of the first user sector available by a user in the first track is disabled, and performs second alternative processing different from the first alternative processing of recording a first parity sector in a second region when writing of the first parity sector acquired by an XOR operation in the first track is disabled.