To solve the following problem: a conventional door locking mechanism is formed by linking all gate bars together by a link, and therefore when the locking mechanism is attacked and when one portion thereof is detached, all the gate bars are detached from each other.

A new door locking mechanism stands an attack on the door by a portable power tool etc., by mounting a buffering spring on a lock shaft, and therefore the gate bars must be individually unlocked. When the door is opened/closed by rotating a key, all the gate bars are linked to the link mechanism in a lump, and the door is opened/closed. On the other hand, when the door is attacked from the outside by the portable power tool etc., by virtue of use of the buffering spring, even if the gate bar is attacked, breakage of the gate bar is not transferred to the link mechanism due to the buffering spring. Thus before opening/closing the door, all the gate bars must be individually attacked and unlocked, and therefore a long time is spent for unlocking the door, which imparts high crime prevention to the locking mechanism.