An RF system is provided that includes an RFID card and a reader-writer device. The RFID card includes a substrate, an RFIC element, an antenna coil, and a deformation sensor. The reader-writer device and the RFID card transmit and receive predetermined information between an antenna coil of the RFID card and an antenna coil of the reader-writer device through a magnetic field. The RFIC element transmits the first signal via the antenna coil when the deformation sensor does not detect bending deformation of the substrate, and the RFIC element transmits the second signal via the antenna coil when the deformation sensor detects the bending deformation of the substrate.