Upon correction, an amplitude measurement unit repeats a process of attaining a write heat state by a write clearance control unit and writing user data to a data region of a measurement track in the state in which a head is positioned to an arbitrary measurement track and then switching the state to a read heat state by a read clearance control unit so as to detect an amplitude of a read signal from a preamble unit in a servo region. A variance calculation unit calculates a variance from the plurality of amplitude measurement values measured by the amplitude measurement unit; and a contact determination unit repeats the measurement process by the amplitude measurement unit while sequentially increasing the base heater control value when the variance is less than a predetermined threshold value and determines contact between the head and the medium when the variance exceeds the threshold value. The write clearance calculation unit calculates the clearance upon write heat of the head from the increased amount of the base heater control value upon contact determination.