To prevent an automobile door locking device from being unlocked by a fraudulent means by improving the mounting rigidity of a key cylinder for the automobile door locking device.

A first cylinder support 3 having a holding hole 4 fitted to the key cylinder 2, and a protrusion 5 for locking a retainer 8, is inserted from the outside of a door outer panel 1 and fitted to the key cylinder 2 projected inside the door outer panel 1, while locking the retainer 8. A second cylinder support 9 is locked to the key cylinder 2 and connected to the first cylinder support 3, and the key cylinder 2 is fixed to the door outer panel 1 in the state of holding the door outer panel 1 by the first cylinder support 3, the retainer 8 and the head part of the key cylinder 2.