A system using an IC tag such as RFID (Radio Frequency Identification) is widely used for information management of articles and the like. As radio-wave-using parts in such a system, an IC tag and a reader/writer antenna are cited. Further, as the reader/writer antenna, a patch antenna or a dipole antenna is generally used. A size of the patch antenna or the dipole antenna is determined by a resonance length that depends on a wavelength, and is therefore commonly larger than a size of the IC tag. When such an antenna resonates, a node occurs in an electric field distribution or a magnetic field distribution. Therefore, in a position that is a node of electric field intensity or magnetic field intensity in a vicinity of an antenna, an area where an IC tag is difficult to read occurs.
As a technique for solving such a problem, conceivable is a technique in which a size of an antenna is reduced to substantially the same size as an IC tag and a portion having strong electric field intensity or magnetic field intensity is caused to be always present in an area where the IC tag is present. One example of an antenna using such a technique is disclosed in Patent Literature 1 (PTL 1).