PURPOSE:To surely read information even when cards are used whose recording density of data parts are different individual cards are used by providing a medium identification information information part in which the information of the recording density of the data part is recorded before the data part of an information storage part. CONSTITUTION:The information storage part 2 is constituted of the medium identification information part 3, the data part 4, and furthermore, a gap part 5 between them. And the recording density of the data part 4 at least following the medium identification information part 3 is stored in the medium identification information part 3 so as to be read surely by a card reader in spite of the recording density of the data part 4. In such a way, it is possible to recognize the recording density of the data part 4 by the reader, and to read the information by the reader surely even when optical cards 1 with different recording density in the data parts 4 are used.
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