With the RFID comprising a transmitting and receiving antenna, a detecting block formed in the circumference of the antenna, and an electronic component connected to the antenna and detecting block to detect breakdown of the detecting block, illegal use can be prevented, matching between the tag antenna and IC chip can also be attained with inclusion of the detecting means, and higher radiation and receiving characteristics of antenna can also be obtained without deterioration of antenna gain. Moreover, the RFID is very effective for keeping security because illegal use of the RFID tag through re-adhesion thereof to an item can be prevented.