To provide a crime preventive instrument which is equipped with a lock at a midpoint of a chain so that the crime preventive door chain can be set from outside a door, and available as an auxiliary lock together with a warning buzzer when the user goes out, to thereby prevent frequent occurring picking.

According to the crime preventive instrument, the chain 4 is attached to the lock 1, and the other end of the chain is connected to an anchor 5 of the crime preventive door chain. Then, a wall-side fixed anchor 8 is arranged at the end of a chain 4" which is hooked and inserted into a hook portion of the lock. Further, the buzzer which sounds upon opening of the door, is employed in addition to the crime preventive instrument, and a switch is operated outside the door by using a remote controller.