Abstract: A locking apparatus for a compartment door operated by a key comprises an outer cylinder fixed in the compartment door, a rotor inserted into the cylinder, a plurality of locking plates inserted into the rotor radially slidably to engage with the cylinder, one or more engaging plates inserted into the rotor radially slidably, a ring surrounding the rotor independently rotatable with respect to the rotor, a lip projected from the ring engageable with the engaging plates, operating means to rotate the ring, and engaging means maintains the door closed and releasable by the rotor. In door-opening operation, the rotor is rotated by the key from a locking position to an releasing position, then the key is removed to engage the ring with rotor. This engagement enables the operating means to rotate the rotor through the ring.