According to one embodiment, a disk storage apparatus includes a disk, a detector, and a controller. The disk includes a first recording area for recording with a first track density, and a second recording area for recording with a second track density lower than the first track density. The detector is configured to detect a variation of an outside environment. The controller is configured to select a nonvolatile memory or the second recording area as a storage destination of write data transferred from a host, based on a content of the variation of the outside environment detected by the detector, and a state of capability or incapability of storage of the nonvolatile memory.