PURPOSE: To obtain an information storage card and its information reader by which the analysis of data is difficult, a forgery/alteration preventing effect is high and handling is facilitated by selectively magnetizing plural areas obtained by segmenting a magnetized layer is a prescribed unit and storing data.

CONSTITUTION: In the magnetized layer 3 consisting of bithmus substitutional magnetic garnet monocrystal, the polarized direction is rotated by 90 degrees by Faraday effect when the layer is magnetized upward. A polarized filter 13 transmits only polarized light which is rotated by 90 degrees. When a case when the magnetized direction of the respective modules is indicated by an upward arrow, for example, is set to be data '1', light is received by a photodetector 14 only in the case of data '1'. Recorded digital data can be read from the pattern of the presence or absence of received light. Namley, the data are read in the card 1 by an operation for irradiating polarized light in the modules and receiving the light passing through it with the photodetector 14 via the polarized filter 13.