There is provided an RF tag that can be mounted in a cavity of a member formed of a conductor having the cavity therein, and has high communication performance. An RF tag 1 of the present invention is an RF tag that is mounted in a cavity 101 of a conductor-made member 100 having the cavity 101 therein, and includes at least a free space antenna 10, a resonance circuit 20, an IC chip 30, a closed space antenna 40, and a substrate 50 for supporting the closed space antenna, a portion of the free space antenna is exposed from the cavity to the outside, and the substrate supports the closed space antenna so that the closed space antenna is not in contact with the inner surface of the conductor-made member. The closed space antenna, the substrate and the conductor-made member forms a capacitor portion C2.
