A wireless IC device has a structure such that the size of a radiation plate and a radiation characteristic may be determined irrespective of an impedance of a wireless IC chip. The wireless IC device includes a wireless IC chip that is arranged to process transmission and reception signals, a spiral matching inductance element and a plane electrode that are located on a surface of a feeder circuit substrate, and a coil-shaped radiation plate located on a radiation substrate. Plane electrodes connected to both ends of the radiation plate are electromagnetically coupled respectively to the inductance element and the plane electrode. The wireless IC chip is operated by a signal received by the radiation plate, and a response signal from the wireless IC chip is radiated outside from the radiation plate.