PURPOSE: To provide a locking device of a door automatically unlocking after a prescribed time by providing a sensor part detecting the locking condition of a locked part, a timer part starting by receiving a signal from the sensor part, and a lock releasing part.

CONSTITUTION: A circular arc shaped door 1 curved in two-dimensional direction is supported with a wall 6 through a rail, and a locking part 2 controlling opening/closing of the door 1 is provided between the door 1 and the wall 6. Next the locking part 2 is constituted of a hook part 2a rotatably supported with the wall 6 side and a receiving metal fitting 2d, and the engaging part 2b on the extreme end of the hook part 2a is engaged with the metal fitting 2d so as to lock the door 1. A shaft 2c is provided with a sensor part 3 detecting the locked condition of the locking part 2, and by being locked, a signal from the sensor part 3 is inputted to a timer part 4 so as to start it. After the lapse of a prescribed time on the timer part 4, the locking part 2 is released with a lock releasing part 5 by receiving a signal from the timer part 4. Hereby, even if a mischief is carried out, the door is automatically unlocked after the prescribed time.