A communication distance difference due to an attached object can be canceled, and an RFID system can be provided which has approximately the same communication distance regardless of an attached position (surface) of a tag. A tag antenna used for such the RFID system is for transmitting/receiving a radio signal to/from an RFID reader/writer in an RFID system has a pair of antenna elements centered on a feeding point and when a carrier wavelength of the radio signal is λ, each of the pair of the antenna elements includes a dipole portion which has a length from the feeding point of approximate λ/4 and a plurality of bending portions as well as a circular polarized wave generation portion linked to an end of the dipole portion.