A disk storage apparatus according to one embodiment includes a head, a storage device, a write module and a controller. The head writes data on a disk. The storage device has a storage area for temporarily storing the data written by the head. The write module writes data to tracks on a disk, while partially overlapping the data with previously written data to adjacent track. The controller detects a drift-off write of the head while writing data, determines a drift-off write area in which the drift-off write is occurred, and protects the data written in the storage area, if the data is written in the drift-off write area.