To prevent forgery or duplication by forming a pattern like specks of marble by using a plurality of pellets of thermoplastic resin having different colors for a recognition information part of a data carrier.

A pellet of, for example, transparent thermoplastic resin to become a base and a pellet of, for example, orange thermoplastic resin for transmitting a light are supplied to an extruder to become a pattern like specks of a marble, and a recognition information part of a data carrier is formed. Thus, the information part 2 of the carrier 1 expresses a pattern 4 like specks of marble of the orange thermoplastic resin for passing the light to the base 3 made of the transparent thermoplastic resin. Accordingly, it is impossible to represent entirely the same size, shape and disposition of the pattern.