To provide a locked lock spin restraining mechanism of a latch lock serving also as a dead bolt capable of preventing the latch lock from being locked while a latch does not return yet and a door is not yet closed, preventing the occurrence of incomplete locking, and improving reliability in locking.

This locked lock spin restraining mechanism of the latch lock 100 serving also as dead bolt lets the latch 25 advancing and backing in accordance with opening and closing of the door function as the dead bolt by restraining backing by the locked locking-unlocking operation member spinning operation. This mechanism is provided with a lock case 21b provided on the door, an energizing means 69 provided in the lock case 21b to energize the latch 25 in the direction of protrusion, a click cam 151 connected with the locking-unlocking operation member to restrain backing of the latch 25 by rotation in the direction of locking, and a locking restraining means 301 provided on the latch 25 and the click cam 151 and arranged at an interference position by backing of the latch 25 to prevent the click cam 151 from spinning in the direction of locking.