To give a demand alarm for locking by voice at the time of going-out by a method wherein an opening signal for a door and a lock operation signal are received and when the latter signal is absent, the former signal is outputted as an operation starting signal.

An opening signal D fetched from a second lead switch 9 is fed to the input terminal of a prohibition gate 12, a lock operation signal L is fetched from a first lead switch 4 and fed to a prohibition gate 12 through a timer 13 for a proper working time. An output signal from the prohibition gate 12 is fed as an operation starting signal to a musical playing apparatus 14. When a door is opened by a user who is about to go out, the opening signal D is generated. Since, when a door is opened from the indoor side, the lock operation signal L is not generated, an output signal from a timer 13 is not fed to the prohibition input terminal of the prohibition gate 12. In this case, an output signal from the prohibition gate 12 is fetched and fed as the operation starting signal to the musical playing apparatus 14 and notification to urge locking is transmitted to a person, being about to go out, by voice.