To prevent illegal unlocking by providing a cylinder lock locked and unlocked with the reception of a signal from a key with a switch and a clutch, and preventing the clutch from being engaged by an illegal method of such as destroying an inner cylinder or the like other than only by the correct signal.

When a key 10 is inserted into a cylinder lock 15, a key switch 13 is pressed to allow power to be fed from a battery 12, thereby generating key information preliminarily set from a transmitter 14. With the reception of this signal at a receiver 16, a main switch 18 is put ON, then power of a main body controller 17 is put ON, and the correctness of key information is determined thereat. If it is correct, a connector/disconnector (clutch) 20 is engaged and when a male thread of key is matched a connection shaft 21 is turned to perform unlocking. Accordingly, even if illegal unlocking is made by pulling an inner cylinder 15b out or destroying it by using a drill, unlocking can not be made because the clutch 20 is not engaged so that the connection shaft is not turned. By a single operation of the key 10 the same effect as that of double locking can be attained. Illegal unlocking can be prevented in this way.