PURPOSE: To manage a commodity having great importance in its beauty, values, etc., with a bar code by marking a bar code on the surface of a ferro-magnetic substrate and adding the marked bar code coated with a non-magnetic substrate to the commodity.

CONSTITUTION: For instance, a bar code thin plate 2 obtained by coating a 'marked bar code' marking a bar code on the surface of a ferromagnetic substance such as iron or nickel with a non-magnetic substance is stuck to the shaft 1 of a golf club. The bar code is magnetically read out by a pen scanner type bar code reader integrally constituted of an Alnico magnet having storing field intensity and a permalloy MR sensor element for detecting a magnetic field with high sensitivity. Since the marked bar code coated with the non- magnetic substance can be read out, a bar code can be utilized even for a commodity to which a bar code can not be used by a convensional method due to its beauty or values.