PURPOSE: To make ID information incapable of being illegaly rewritten by magnetically recording plural pieces of ID factor information and setting a superimposed waveform of read waveforms of these pieces of the ID factor information on the ID information.

CONSTITUTION: Three tracks for recording information are set on a recording surface formed with magnetic substance all over the surface of a prepaid card. The 1st track is recorded with card information, and the 2nd track with distinctive cipher information featuring the ID information to be recorded on the next 3rd track. By utilizing the magnetic layer 14 consisting of two magnetic layers of upper layer 14a and a lower layer 14b, the 3rd track 13 is magnetically recorded with analog waveforms of the ID factor information in the layers 14a and 14b respectively, thus the superimposed waveform of these pieces of the information constituting the ID information. When the ID factor information in the upper layer 14a is rewritten, a phase difference is caused by this rewriting, so that a waveform of the sum is changed, and hence a phase difference between the information of layers 14a and 14b and an output level are changed at random. Consequently, high security can thus be obtained.