A magnetic disk device includes a disk that includes a plurality of tracks and magnetically stores therein data; a magnetic head that reads and writes data on the tracks; a data writing unit that classifies sectors along one track into a plurality of sector groups and writes to a physical address of each of the sector groups data of a logical address that is different from a logical address corresponding to the physical address in same track; and a first nonvolatile memory that stores therein a conversion table of the logical address and the physical address.