A level peak-acquiring unit acquires a peak of a signal level during a calibration wherein a heater power is increased from zero to a predetermined power. A sample acquiring unit acquires in a sampling range, a sample of a combination of the heater power and the signal level. A linear function-determining unit determines a linear function that approximates from the sample, a relation between the heater power and the signal level. Based on the peak of the signal level and the linear function, a control Touch Down Point (TDP)-calculating unit calculates the heater power corresponding to the peak of the signal level and treats the calculated heater power as a control touchdown point. Then, the control TDP-calculating unit uses the control touchdown point to convert into a linear function of the heater power and spacing, the linear function of the heater power and the signal level.