The invention discloses an automatic binding device which comprises a clamping main body and a binding belt bin arranged on the side wall of the clamping main body, a sliding way is arranged on the clamping main body, and the sliding way is communicated with the inner wall of the binding belt bin; the clamping main body is used for wrapping the outer wall of an object to be bound; a pushing part is arranged on the inner wall of the sliding way and can push the cable tie to move along the sliding way under the power action of a first motor, the cable tie is taken out after the cable tie moves to be larger than one circle along the sliding way, and at the moment, the cable tie is located on the outer wall of an object to be bound. By arranging the clamping body capable of being opened and closed, the technical problem that it is difficult for a single person to conveniently bind objects such as a bridge cover plate is solved, and the purpose that binding operation can be completed by the single person is achieved; the technical problems that traditional manual binding is low in efficiency, and firmness and consistency are difficult to guarantee are solved, and the technical purposes that binding belt conveying is stable, binding operation is convenient, fast and efficient, and binding quality is more uniform are achieved.