A wireless IC device includes a wireless IC chip for processing a transmission/reception signal, a printed wiring circuit board on which the wireless IC chip is mounted, a ground electrode disposed on the circuit board, and a substantially loop-shaped electrode that is electrically conducted to the wireless IC chip and disposed on the circuit board so as to be coupled to the ground electrode by an electromagnetic field. The ground electrode is coupled to the wireless IC chip via the substantially loop-shaped electrode to transmit/receive a radio frequency signal. A feeder circuit board including a resonant circuit and/or a matching circuit may be interposed between the wireless IC chip and the substantially loop-shaped electrode.