Abstract: To assure that door locking can reliably be achieved, two permanent magnets are arranged for a locking device. One of the permanent magnets, i.e., a first permanent magnet is carried on one end of a trigger member of which central part is turnably supported in a lock box, while the other one, i.e., a second permanent magnet is disposed on a door frame at the position located in alignment with the first permanent magnet when a door is closed. The magnetic pole of the first permanent magnet is coincident with that of the second permanent magnet. When the door is closed, the first permanent magnet is displaced away from the second permanent magnet by the magnetic repulsive force appearing between both the permanent magnets, causing the trigger member to be disengaged from an engagement lever made integral with a control gear, resulting in the dead bolt becoming operatively free.