An RF tag includes an inlay comprising an IC chip and an antenna, a planar auxiliary antenna laminated on the inlay in an insulating state to the inlay, and a substrate on which the inlay and the auxiliary antenna are laminated. The auxiliary antenna is formed into a rectangular planar shape including long sides each having a length of substantially ¼ of a wavelength of a radio wave frequency of the inlay, and has a cutout part which divides one of the long sides into two parts each having a length of substantially ⅛ of the wavelength of the radio wave frequency of the inlay. The cutout part is formed into a concave shape which is opened in an edge portion of the one of the long sides and has a predetermined width and depth to allow the IC chip of the inlay to be disposed therein.