To provide a device for preventing a failure of locking, which can prevent a person from forgetting to lock when going out.

The device for preventing the failure of a locking comprises container 1 of an electronic system attached to a door 5, and a key holder 7 having a remote control function. The container 1 has a built-in circuit connecting power supply, a power switch 2, a sounder, a radio-wave-receiving part, and a sound-cutting switch. The key holder 7 holds a knob therein and is provided with a radio-wave-oscillation-switch pressing part, which is parallel with the sword part of the key held therein and a transmitting antenna 8. When the door 5 is opened, the sound is generated from inside the container 1, and the sound keeps coming out even when the door 5 is closed. When the key is inserted into a key hole, the radio-wave-oscillation-switch pressing part backs off, and acts on a radio-wave-oscillation part. Then a sound-stop signal is sent to the container 1, and the radio-wave-receiving part of the container 1 receives the sound-stop signal. Then the switch for cutting the sound operates, and the sound stops.