According to one embodiment, a disk storage apparatus includes a magnetic head, a detector, a calculator, and a decision module. The magnetic head has a high-frequency assisted element disposed close to a main magnetic pole that generates a recording magnetic field for perpendicular magnetic recording, the high-frequency assisted element applying a high-frequency magnetic field onto a magnetic disk during data recording. The detector detects an electrical resistance of the high-frequency assisted element. The calculator calculates time axis data indicative of a variation, on a time axis, in the electrical resistance value detected by the detector. The decision module determines whether the high-frequency assisted elements is malfunctioning based on the time axis data.