An information processing system includes an information bearing medium (2) and an information reading unit (3). The information bearing medium (2) has a two-dimensional array of unit data zones (11). Marks (13) are provided on some of the unit data zones (11) so as to form a digital code. Mark patterns of any two Y-directional adjacent unit data zone strings (14a, 14b, 14c, 14d) based on the arrangement of marks (13) in an X-direction differ from each other. The information reading unit (3) generates a data string on the basis of a unit signal formed from a plurality of signals output from a group of detection units (21) that detect the marks (13) in synchronization and recognizes the digital code of the information bearing medium (2) on the basis of a group of the data strings sequentially obtained from the array of the unit data zones (11).