PURPOSE: To form a bar code as visible information by later heating a thermal coloring layer formed on an information recording medium.

CONSTITUTION: In the information recording medium for recording information on an infrared ray reflecting layer 24 by an infrared ray absorbing bar code consisting of an infrared ray absorbing material, the infrared ray absorbing bar code 18 and a dummy infrared ray transmitting bar code 20 consisting of an infrared ray transmitting material are previously formed, an infrared ray transmitting bar code 160 is additionally formed by heating the thermal coloring layer 16 and visible information is recorded by combining these bar codes.