Control circuit and information storage device

An information storage device comprising:

• a head slider having a flying height control mechanism and a recording and reproducing head;
• a recording medium in which information is recorded and reproduced by the recording and reproducing head;
• and
• a control circuit comprising:
• a signal strength detection section that detects strength of a reproduction signal of the recording and reproducing head;
• a low frequency oscillation section that superimposes a low frequency to the head slider;
• a limit flying height judgment section that determines a limit flying height of the head slider through comparison of a low frequency overlay signal where the low frequency is superposed to the head slider and a low frequency overlay signal obtained from a reproduction signal of the recording and reproducing head when the low frequency is superposed to the head slider;
• a comparator that computes an output strength difference between a signal strength output from the signal strength detection section and a reference signal strength on a reference flying height;
• and a flying height control section that receives the output strength difference from the comparator and the limit flying height from the limit flying height judgment section, and controls the flying height of the head slider with the flying height control mechanism to the reference flying height in accordance with the output strength difference and the limit flying height.