Abstract: A response permission command is transmitted from a reader/writer, thereby setting all of data carriers to a response possible state. Subsequently, a data return command is transmitted, thereby returning data for collation on a bit unit basis. The reader/writer transmits a data collation command of, for example, bit 0 to each of the data carriers when recognizing the return of the data in which bits 0 and 1 mixedly exist. When an own return bit coincides with a collation bit, each of the data carrier judges that the collation succeeds and returns a next bit for collation. When they don't coincide, however, a state of the data carrier is switched to a response inhibition state. By repeating such processes with respect to all of the bits of the data for collation, only one data carrier finally remains in a response possible state and generates an access permission command, thereby performing the reading or writing operation.