A wireless IC device includes a wireless IC chip arranged to process a transmission/received signal, a matching inductance element and a planar electrode which are provided on the surface of a feeder circuit board formed by a flexible dielectric, and a loop-shaped radiation plate provided on the undersurface of the feeder circuit board. Both ends of the radiation plate are coupled to a resonance circuit including an inductance element by electromagnetic field coupling. The wireless IC chip is operated using a signal received by the radiation plate. A response signal transmitted from the wireless IC chip is externally transmitted from the radiation plate.