To provide a locking device and a key control system using the locking device without hindering the control and operation by an owner (house owner), a caretaker, or the like, and also capable of reducing the control expenses.

Respective locks A to D provided in the entrance doors of the respective dwelling facilities of a building can be locked or unlocked by the respective exclusive keys F to H. Each of the locks A to D has a principal mechanism part 11 and an emergency mechanism part 12, and the principal mechanism part 11 can be locked and unlocked both by the exclusive keys F and H and by the master key M. The locking and unlocking of the emergency mechanism part 12 can be done by the master key M, and in the locking condition of the emergency mechanism part 12 by means of the master key M, the locks A to D can not be unlocked by means of the exclusive keys F to H.