Magnetic disk device

A magnetic disk device comprising:

• a disk having a plurality of bands each including a plurality of tracks, each of the plurality of tracks including a plurality of sectors;
• a write head writing data to the disk;
• a write processing unit selecting shingled magnetic recording of overwriting data to the plurality of tracks in an overwrite direction parallel to a radial direction of the disk, and causing the write head to write data to each of the plurality of bands;
• a determination unit determining whether a quality-degraded recording sector in which quality of recorded data is lower than a reference level exists in all recording sectors to which data is written, in each of the plurality of bands;
• and
• a refresh processing unit, if it is determined that a target band including the quality-degraded recording sector exists in the plurality of bands, reading target data of a plurality of target recording sectors, which is a target of refresh, among all the recording sectors of the target band, rewriting target data to the plurality of target recording sectors, and refreshing the plurality of target recording sectors,
• wherein
• the plurality of target recording sectors include the quality-degraded recording sector, and
• the number of the plurality of target recording sectors is less than the number of all the recording sectors, in the target band.