PURPOSE: To provide a locking device for offertory box in which the theft of an offertory can be prevented, and a lock is difficult to break.

CONSTITUTION: A key hole 22 to which a key can be inserted and an opening having an openable and closable lid are provided on a part of a side plate 2. A lock plate 10 movable between the position for locking the lid and the position evacuated from the lock position is provided on the inside of the side plate 2. A cam surface 11b opposed to the key hole 22 and extended obliquely is formed on the lock plate 10, so that the lock plate 10 is moved from the lock position to the evacuated position by engaging the key with the cam surface 11b. Further, the lock plate 10 has an arresting part 11a engaged with a key other than a specified form to arrest the movement of the lock plate.