A main controller, such as a CPU, causes a runout detector to relearn a runout component using as an initial value a learned value for a runout component of a disk runout that may occur as a disk rotates, the learned value being acquired during manufacture of a disk drive. The learned value for the runout component used as the initial value is saved to a nonvolatile storage device. The main controller calculates a disk shift amount on the basis of a runout component obtained through relearning (that is, a relearned value) and the learned value acquired during the manufacture of the disk drive and used as the initial value.