According to one embodiment, a hard disk drive includes a detecting circuit configured to detect abnormality of a supply voltage. The hard disk drive also includes a refresh controller configured to, when the abnormality of the supply voltage is detected during a data refresh process in sector units to a magnetic disk, finish the data refresh process to a sector after writing of data to a data area is finished, the data area to which the writing is performed when the abnormality of the supply voltage is detected, without stepping over a servo area.