Patent ID: 8605378

Claim:
An inspection device for a magnetic disk or a magnetic head which measures a characteristic of the magnetic disk or the magnetic head by controlling the magnetic head based on servo information written on the magnetic disk and reading or writing a signal from/to the magnetic disk, comprising: a servo demodulation unit which demodulates the servo information read out from the magnetic disk; a PLL clock generating unit which generates a reference clock corresponding to the frequency of the servo information read out from the magnetic disk and supplies the reference clock to the servo demodulation unit; and a tester control unit which controls the operation of the inspection device, wherein: the PLL clock generating unit includes an eccentricity correction circuit for correcting the frequency of the reference clock depending on an eccentricity of the magnetic disk, and the tester control unit generates correction data for correcting the frequency of the reference clock, multiplies the correction data by the inverse of a transfer function of the PLL clock generating unit, and supplies the product to the eccentricity correction circuit.