| 摘要 |
A magnetic disk device of an embodiment includes a magnetic disk, a magnetic head, a laser-beam-intensity control unit, a reproduced-signal detecting unit, and a magnetic-disk evaluating unit. The magnetic head reads a signal recorded in the magnetic disk, or performs magnetic recording while irradiating a laser beam onto the magnetic disk. The laser-beam-intensity control unit controls the intensity of the laser beam. The reproduced-signal detecting unit detects the signal read by the magnetic head. The magnetic-disk evaluating unit evaluates the signal read from the magnetic head, on the basis of a relation between a noise level detected from the signal read by the magnetic head, and the intensity of the laser beam.
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