An information processing system includes an information bearing medium and an information reading unit. The information bearing medium has a two-dimensional array of unit data zones. Marks are provided on some of the unit data zones so as to form a digital code. Mark patterns of any two Y-directional adjacent unit data zone strings based on the arrangement of marks in an X-direction differ from each other. The information reading unit generates a data string on the basis of a unit signal formed from a plurality of signals output from a group of detection units that detect the marks in synchronization and recognizes the digital code of the information bearing medium on the basis of a group of the data strings sequentially obtained from the array of the unit data zones.