Embodiments relate to a tag device, a reader device, and a radio frequency identification (RFID) system. The Q embodiment provides a tag device comprising: a reception module converting a received high frequency signal into a scale level, and Q converting the converted scale level into a digital signal to output the same; a transmission module modulating a transmission signal M to output the same; and a controller controlling the reception module and the transmission module. The tag device communicates with the reader device through wireless short distance communication.