A wireless IC device comprising: a resin member including a first surface and a second surface that faces the first surface; a substrate including a first principal surface and a second principal surface that faces the first principal surface, the substrate being embedded in the resin member so that the second principal surface is at the second-surface side of the resin member; an RFIC element mounted on the first principal surface of the substrate; and a coil antenna connected to the RFIC element, wherein the coil antenna includes a first linear conductor pattern (20A-20G) formed on the second surface of the resin member, a first metal post (30A-30F) including a first end and a second end that extend to the first surface and the second surface of the resin member, the first end being connected to the first linear conductor pattern (20A-20G), a second metal post (40A-40F) including a first end and a second end that extend to the first surface and the second surface of the resin member, the first end being connected to the first linear conductor pattern (20A-20G), and a second linear conductor pattern (50A-50F) formed on the first surface of the resin member, the second linear conductor pattern (50A-50F) connecting the second end of the first metal post (30A-30F) and the second end of the second metal post (40A-40F) to each other, characterized in that the substrate is embedded in the resin member so that the second principal surface of the substrate and the second surface of the resin member are flush with each other, wherein the first linear conductor pattern (20A-20G) is formed so as to extend over the second principal surface of the substrate and the second surface of the resin member, and wherein the RFIC element is disposed in the coil antenna and is connected to the first linear conductor pattern (20A-20G) by an interlayer conductor (11A, 12A) formed in the substrate. a resin member including a first surface and a second surface that faces the first surface; a substrate including a first principal surface and a second principal surface that faces the first principal surface, the substrate being embedded in the resin member so that the second principal surface is at the second-surface side of the resin member; an RFIC element mounted on the first principal surface of the substrate; and a coil antenna connected to the RFIC element, wherein the coil antenna includes a first linear conductor pattern (20A-20G) formed on the second surface of the resin member, a first metal post (30A-30F) including a first end and a second end that extend to the first surface and the second surface of the resin member, the first end being connected to the first linear conductor pattern (20A-20G), a second metal post (40A-40F) including a first end and a second end that extend to the first surface and the second surface of the resin member, the first end being connected to the first linear conductor pattern (20A-20G), and a second linear conductor pattern (50A-50F) formed on the first surface of the resin member, the second linear conductor pattern (50A-50F) connecting the second end of the first metal post (30A-30F) and the second end of the second metal post (40A-40F) to each other, characterized in that the substrate is embedded in the resin member so that the second principal surface of the substrate and the second surface of the resin member are flush with each other, wherein the first linear conductor pattern (20A-20G) is formed so as to extend over the second principal surface of the substrate and the second surface of the resin member, and wherein the RFIC element is disposed in the coil antenna and is connected to the first linear conductor pattern (20A-20G) by an interlayer conductor (11A, 12A) formed in the substrate. a first linear conductor pattern (20A-20G) formed on the second surface of the resin member, a first metal post (30A-30F) including a first end and a second end that extend to the first surface and the second surface of the resin member, the first end being connected to the first linear conductor pattern (20A-20G), a second metal post (40A-40F) including a first end and a second end that extend to the first surface and the second surface of the resin member, the first end being connected to the first linear conductor pattern (20A-20G), and a second linear conductor pattern (50A-50F) formed on the first surface of the resin member, the second linear conductor pattern (50A-50F) connecting the second end of the first metal post (30A-30F) and the second end of the second metal post (40A-40F) to each other, characterized in that the substrate is embedded in the resin member so that the second principal surface of the substrate and the second surface of the resin member are flush with each other, wherein the first linear conductor pattern (20A-20G) is formed so as to extend over the second principal surface of the substrate and the second surface of the resin member, and wherein the RFIC element is disposed in the coil antenna and is connected to the first linear conductor pattern (20A-20G) by an interlayer conductor (11A, 12A) formed in the substrate.