PURPOSE: To prevent unlocking from the outside even if the normal key is used so as to prevent intrusion from the outside by adding a security device to the moving pipe of a door lock, and operating a security knob provided on an inner handle.

CONSTITUTION: A security device 70 is additionally installed within the moving pipe 40 of a door lock which is unlocked by a key operation from an outer handle 10 or by rotation of an inner handle 20. The inner handle 20 is provided with a security knob 42 in addition to a push knob 48 and is pushed in to actuate the security device 70. Thus when the security knob is operated from the inside, the door lock cannot be undone from the outside even if the normal key is used.