According to one embodiment, a magnetic disk device includes a read control system that extracts scrambled data from media data read from a medium and inspection data associated with a seed value at the time of write, generates inspection data for data extracted from the media data, obtains from the inspection data and inspection data extracted from the media data, a seed value associated with both, compares this seed value with the seed value expected by the controller, and evaluates, when the comparison result is a mismatch, the data as an error, whereas when match, descrambles the data extracted from the media data using the seed value.