A wireless IC device includes a resin member including first and second surfaces, a substrate including first and second principal surfaces, a coil antenna provided in the resin member, and an RFIC element mounted on the substrate and connected to the coil antenna. The substrate is embedded in the resin member so that the second principal surface is at a second surface side. The coil antenna is defined by first linear conductor patterns on the second surface, first metal posts extending between the first and second surfaces, second metal posts extending between the first and second surfaces, and second linear conductor patterns on the first surface. The RFIC element is disposed in the coil antenna.