Rfid tag and automatic recognition system

An RFID tag having a resin substrate, an IC chip positioned in the center section on the substrate, a single-layer antenna for forming an electric closed circuit by connecting with the IC chip and positioned in the peripheral section of the IC chip, and a sealing material for sealing the IC chip and the antenna, wherein the antenna is a coil antenna or a loop antenna, the resonant frequency (f0) of the antenna is the operating frequency of the IC chip or thereabouts, the operating frequency of the IC chip is 13.56 MHz-2.45 GHz, or 0.86-0.96 GHz, and the size of the RFID tag is 13 mm or less in length, 13 mm or less in width, and 1.0 mm or less in height; and an automatic recognition system using the same.