The invention provides an automatic polishing device. The automatic polishing device comprises a conveying belt, a supporting frame, telescopic rods, rotating shafts, grinding wheels, first motors, second motors, a processor and a device body, wherein the conveying belt is arranged above the device body, the four second motors are arranged in the device body, the telescopic rods are arranged at the output ends of the second motors, the telescopic rods are parallel to the horizontal plane, the free ends of the telescopic rods are fixedly connected with the bottom of the supporting frame, the first motors are arranged in the supporting frame, the rotating shafts are arranged at the output ends of the first motors, the grinding wheels are arranged on the tops of the rotating shafts, the processor is arranged on the device body, and the processor controls start and stop of the first motors and the second motors through connecting lines. The automatic polishing device can polish burrs on the edges of metal plates with different widths and has the advantages of being simple in structure, convenient to maintain, high in production efficiency and the like.