A memory control unit reads pieces of bit data to be checked by a check pulse to be received next by an antenna, the pieces of bit data being stored in a memory and forming unique data. The memory control unit operates a switch based on the content of the pieces of bit data. A reflection electrode reflects a surface acoustic wave excited by an interdigital electrode when both terminals of the reflection electrode are opened by the switch. The reflection electrode passes the surface acoustic wave when both terminals of the reflection electrode are short-circuited by the switch. The present invention is applicable to RFID systems using SAW.