An RFID antenna is arranged in the vicinity of a metal portion of and on an outer surface side of a casing of a communication terminal device. The RFID antenna includes a magnetic core, and a coil conductor that is wound around the magnetic core. The coil conductor includes a first conductor portion positioned on a first main surface side of the magnetic core and a second conductor portion positioned on the second main surface side of the magnetic core and arranged at a different position than the first conductor portion when viewed in plan from the direction of the first and second main surfaces, and the coil conductor is arranged such that the first main surface side of the magnetic core is on the metal portion side and such that the first conductor portion of the coil conductor faces a leading end portion of the casing.