An information storage apparatus having a disk medium 3 with data recording areas 203 along a plurality of tracks concentrically arranged, a head 4 for recording and reproducing data on tracks of the disk medium, an actuator 5 for moving the head to a desired track among the plurality of tracks, and an electric circuit 7 for controlling recording and reproducing and for detecting the distance from a recorded magnetization pattern on the adjacent tracks in the radial direction by detecting already recorded signals of adjacent tracks during data recording. By use of this constitution, even if the track density is increased, the upper limit of the threshold value setting range in the function for preventing from offtrack recording of the information storage apparatus can be increased and a high track density of the information storage apparatus can be easily realized.