A cage having an automatic door is described. A front side of the cage is provided with a door panel. A top edge of the door panel is hingely attached to the cage. A bottom edge of the door panel is attached to the cage through a spring. A pedal is provided on a bottom surface of the cage. A front side of the pedal is hingely attached to the cage. The pedal is connected with a connecting rod. An upper end of the connecting rod extends upward and forward along a sidewall of the cage and is bent towards an exterior of the door panel. A spring supporting seat is fixed on the sidewall of the cage. Said spring supporting seat is connected with a spring. The connecting rod is fixedly provided with a spring contact point. Spring can move the connecting rod up toward the top of the cage and forward toward the front of the cage to lift up the pedal. A hook is fixedly provided on an outer surface of the door panel. An opening of the hook faces the top of the cage. When the door panel is in its fully open position, a bending portion of the upper end of the connecting rod locks into the hook. When the pedal is pressed down, the connecting rod is pulled downwardly and detached from the hook. The door panel moves down automatically to close the cage. In case of trigger mechanism failure, the door panel can be lifted by one hand, and quickly and automatically locks in position to restart, no other manual adjustment is needed.
