To provide a core member by which radio waves are hard to pass in a thickness direction and which fully demonstrates its function even when it is directly attached to an article without using a spacer.

The core member 12 is formed by alternately laminating a magnetic layer 12a and a non-magnetic layer 12b. The non-magnetic layer 12b is a film consisting of polyimide, polytetrafluoroethylene, phenol or epoxy. The magnetic layer 12a is preferably formed of a complex material or coating film. A tag is provided with the core member 12 attached to the article 11 and formed like a plate, a coil main body 13 spirally wound so that it is laminated on the surface of the core member 12 and an IC chip 14 electrically connected with the coil main body 13 and constituted so that information unique to the article 11 is stored. The coil main body 13 is spirally wound on a base material consisting of resin film and laminated on the surface of the core member 12 via the base material.