To make it possible to enhance security and eliminate the need for a pair control of a key device (a detected device) and a locking device (a detection device).

There are provided a detected device 1 having a first memory section 5a having a first radio transmitter and receiver section 4, a first signal processor 3 and a first memory section which stores identification signals and a detection device 10 having a second radio transmitter and receiver section 11, a second signal processor 12, a second memory section 13 which stores identification signals and a random number generator 14. When the detection device 10 receives a response demand signal from the detected device 1, the detection device 10 is arranged to transmit a random number signal X from the random number generator 14. When the detected device 1 receives the random number signal X, an identification signal ID stored in the first memory 5 is coded with the random number signal. This coded identification signal is transmitted to the detection signal 10. In the detection device 10, the coded identification signal is deciphered and this deciphered identification signal is checked so as to see whether or not it is identical to the identification signal stored in the second memory 13.