The utility model provides an automatic discharging device. A hopper is fixed in the middle of a vehicle frame, the lower portion of the vehicle frame is connected with a pin through a bearing, a fan-shaped rotational material door is hung on the pin, the lower edge of the rotational material door is provided with a door shifting rod, wheels connected with a transmission mechanism are arranged at four corners of the vehicle frame, a limiting block is arranged at one end of a track bearing the wheels, and a backstop is arranged on the upper edge of a receiving trough. When a discharging vehicle moves to the door shifting rod and makes contact with the backstop of the receiving trough, the rotational material door is driven to rotate backward through the door shifting rod so as to open a discharging port; when the discharging vehicle moves to the limiting block and is stopped, the discharging port is opened completely; after discharging is finished, the discharging vehicle runs in a reversing mode, the door shifting rod breaks away from the backstop, the rotational material door droops and blocks off the discharging port, and the discharging vehicle is used for the next charging and discharging process. The automatic discharging device can achieve whole-course automation of charging, collecting and discharging, save a great deal of manpower and cost, relieve labor intensity, improve working efficiency and equipment operation efficiency, and be suitable for the situations that a route is fixed, charging is conducted at multiple spots and discharging is conducted at a fixed spot.