To provide a door self-unlocking device capable of unlocking a door by the predetermined seismic intensity or more of earthquake without using electric power and preventing the door from being unlocked by such earthquake generating small tremor and vibration that cause no destruction of a private house.

In this door self-unlocking device, a swing adjusting screw 43 is adjusted to make a pulling-off lever 28 push and move the swing adjusting screw when swing of a weight 40 exceeds the predetermined swing or more due to vibration of earthquake, the swing adjusting screw 43 is pushed and moved by the predetermined swing or more by adjusting the swing adjusting screw, a lock lever 41 is turned in the direction for releasing locking of a slide rod 19, and a wire 11 is pulled by a drive spring 20 to unlock the door.