Automatic door locking device

The invention relates to an automatic door locking device. An adjusting rack is arranged in space formed between a lock cylinder upper cover and a lock cylinder lower cover, the adjusting rack is in sliding match with a sliding guide rail arranged on the lock cylinder lower cover, an adjusting guide rail is arranged on the adjusting rack, and a locking block is arranged on the side of the adjusting guide rail, the adjusting guide rail adjusts the height of the locking block to drive up-and-down motion of the locking block to achieve unlocking or locking with a spring bolt. According to the technical solution of the automatic door locking device, when a main control panel gives a locking signal, an electromagnetic coil is charged with forward direct current to push a permanent magnet to move so as to drive the adjusting rack to move, the adjusting guide rail moves to a low potential, and the locking block moves downwards under the elastic action of the moving contact switch reed to limit the spring bolt, so th