To provide a locking mechanism for door capable of utilizing a space inside a lock box further effectively and increasing suppressing force of a braking lever.

In this locking mechanism for door for locking a latch member 2 by a distal end part 5a of a locking lever 5 supported in the lock box 1 through a first support shaft 4 when locking, the locking lever 5 has an arm part 5b provided continuously and upward by rising from behind more than the first support shaft 4 and crossing a latch bolt 2b of the latch member 2. In addition, the hammer type braking lever 7 supported through a second support shaft 8 is provided on the opposite side to the first support shaft 4 to press a receiving part 5d provided in an upper end part of an arm part 5b by a lower end part of the braking lever 7 always. For this reason, even if exciting force acts on the lock box from the outside and the locking lever 5 attempts to leave an engaging part 6 of the latch member 2, it is suppressed or braked by each weight of the arm part 5b of the locking lever 5 and the braking lever 7.