A wireless IC device and an electronic apparatus are obtained, which can achieve miniaturization and improve the gain of a radiator plate (electrode) without providing a dedicated antenna. A wireless IC device is provided, in which a loop electrode is provided in a ground electrode provided on a printed wiring circuit board, and in which a wireless IC chip that processes a transmission/reception signal or an electromagnetic coupling module is coupled to the loop electrode. The ground electrode is coupled to the wireless IC chip or the electromagnetic coupling module via the loop electrode, and transmits or receives a high-frequency signal. The ground electrode is formed with a slit for adjusting a resonant frequency thereof.