To provide a guide mechanism for a drop rod, by which even a long drop rod 5 can be easily and accurately guided, and also construction can be facilitated.

This drop lock 3 is so constructed that a drop lock 3 is provided in the inside of a hollow vertical doorframe 2, and a drop rod 5 is formed in such a manner as to be projected downward from the lower end of a vertical doorframe 2. A cap 13 is fitted to the lower end of the vertical doorframe 2, a through hole for passing the drop rod 5' is bored in the cap 13, and a guide cylinder for guiding the drop rod 5 is continuously formed on the upper part of the through hole.