The heads have write head elements which record data onto a disk medium capable of coping with perpendicular magnetic recording and read head elements which reproduce data. The monitored band detecting unit sets a frequency band in a range from the signal band of the write data signal to the error rate worsening band on a lower level in which the error rate worsens as a monitored band, and detects a signal in the monitored band from among write data entered into the write amplifier. The determining unit discontinues the recording operation of the write amplifier upon determination that a detection signal of the monitored band detected by the monitored band detecting unit is larger than a prescribed threshold value and outputs a determination signal from the fault terminal to generate a fault event.