PURPOSE: To provide a mechanical door lock device which has a simple and inexpensive structure, allows checking whether the door is locked or unlocked and whether any article is enclosed therein without providing any special device, and eliminates the need for taking measures against power failure, etc.

CONSTITUTION: A lock plate 7 is rotated by a key 9 inserted in a lock 8, and is locked in an oblong hole 6 in the door 3. A rocking arm 15 is secured to a shaft member 13 rotated by the placing of an article on the floor face, and is provided with a latching rod 16 which keeps the lock plate 7 from rotating. A latching arm 21 that keeps the lock plate 7 from rotating is provided integrally with a closure detecting bar 19 which is displaced backward by the closing of the door 3, and the key 9 is allowed to be pushed into and pulled out of the lock 8 only when the door is locked.