To provide a reader/writer capable of obtaining a higher S/N ratio than before in non-contact data communication.

A reader/writer antenna coil is provided with such a positional relationship that with an IC card stored in a designated position, an IC chip built in the IC card is positioned on the outside of a space corresponding position enclosed with a coil, and a card antenna exists in the space corresponding position. By this arrangement, out of the magnetic flux generated by the card antenna coil and the reader/writer antenna coil in non-contact data communication, the magnetic flux penetrating through the IC chip is cut down. Accordingly, induced noise having no relation with the communication data, which is generated in the internal wiring of the IC chip, can be reduced. As a result, the S/N ratio of communication can be improved.