PURPOSE: To simplify card control by removing stored information if the information read of a magnetic card agrees with the information stored of the card when a lock is in a locking state, and then unlocking the lock.

CONSTITUTION: While an automatic lock 1 is unlocked, a person given admittance inserts into a card reader 2 a magnetic card 3 that he owns for another purpose, so that information stored in the card 3 is read by the reader 2. The information stored in the card 3 is correctly read by the reader 2 and stored in the memory portion 4 and the person given admittance is informed of this process and also the door is locked by a lock 1. To unlock the lock 1, the person inserts the card 3 into the reader 2 again so that the reader 2 reads the information. Then the control portion 6 compares the information read with the information stored and, when they agree with each other, informs the person of the agreement via an information device 5 and clears out information stored in the memory portion 4 and unlocks the lock 1.