For making difficult to copy data of a RFID tag, while enabling to detect it when copying the data, easily, but without exerting ill influences upon the existing specification thereof, within the RFID tag 100 is provided a readout exclusive bank, other than banks provided in accordance with the existing specification. RFID identification information is stored into the readout exclusive bank of the RFID tag 100, when the RFID tag 100 is shipped out of a maker. A user who wishes to guarantee properness of UII data produces cryptograph calculation result data through encrypting the RFID identification information and the UII data, when writing the UII data into the RFID tag 100, and stores the cryptograph calculation result data into a USER bank within the RFID tag 100. Other users, who wish to read out the UII data from the RFID tag 100, read out the RFID identification information and the UII data from the RFID tag 10, so as to conduct cryptography calculation thereon, and can make determination on whether the data stored in the RFID tag is proper one or not, by making a check upon coincidence between the calculation result and the calculation result data stored in the RFID tag 100.