Embodiments in accordance with the present invention increase the possibility that a servo track in which servo data is defective may be detected, greatly decreasing the possibility that a write error may occur during use by a user. According to one embodiment of the present invention, a defective area management method for a data storage device is provided. The data storage device comprises a head in which positions of read and write elements differ from each other in the radial direction of a disk. A defective area management method performs positioning of the head by reading out servo data written on the disk using the read element. The defective area management method comprises the steps of performing data write processing by use of the write element with the read element being positioned at a target position at which normal data reading is performed; and registering areas, as an error area, in a data track in which normal data writing is performed using a servo track including the target position if a predetermined error occurs in the data write processing.