An RF tag has an inlay with an IC chip and an antenna, a planar auxiliary antenna laminated on the inlay in an insulating state, a dielectric constant regulation plate which becomes a base on which the inlay including the auxiliary antenna laminated thereon is mounted, and functions as a dielectric constant regulation layer for the mounted inlay, and a case which receives the dielectric constant regulation plate in a state where the inlay including the auxiliary antenna laminated thereon is mounted. The dielectric constant regulation plate is formed into a shape which allows the dielectric constant regulation plate to be attachably/detachably and non-movably engaged in the case and which allows the dielectric constant regulation plate to have a predetermined dielectric constant which regulates communication characteristics of the inlay including the auxiliary antenna laminated thereon.