NOVELTY - The automatic mixer comprises a top rail covering vertical rails (1) that are arranged into two columns on a lateral side of a compost grinder, a sliding seat (21) arranged under two ends of a horizontal rail (2) to shift the seat horizontally along the vertical rails, carriers (3) arranged into the horizontal rail, a roller wheel arrangement arranged on the carriers until the carrier shifts along horizontal rails, and mixer units having a mixing plate (4) and a chain belt. The mixing plate is hinged on the carrier that is lowered and raised by elevation tools.    USE - The automatic mixer is useful for mixing and decomposing an organic compost in a grinder.    ADVANTAGE - The automatic mixer accelerates the fermentation of compost and increases the output and quality of the compost by efficient mixing and decomposing the compost.    DETAILED DESCRIPTION - The automatic mixer comprises a top rail covering vertical rails (1) that are arranged into two columns on a lateral side of a compost grinder, a sliding seat (21) arranged under two ends of a horizontal rail (2) to shift the seat horizontally along the vertical rails, carriers (3) arranged into the horizontal rail, a roller wheel arrangement arranged on the carriers until the carrier shifts along horizontal rails, and mixer units having a mixing plate (4) and a chain belt. The mixing plate is hinged on the carrier that is lowered and raised by elevation tools. The chain belt is installed on an active gear mounted on the mixing plate and a passive gear mounted on the opposite ends of the mixing plate. The active gear is driven by a main motor belt so that the winding number of the chain belt and rakes are arranged in a chain belt around the mixing plate. The elevation tool is steel rail strap. A mechanism of roller wheel arrangement is formed in mixing plate to arrange the distance between passive gear and opposite ends of the plate, and includes a seat retainer mounted on mixing plate, a screw retainer mounted on a holder and a pair of closed locator.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic lateral view of a mixer.    Vertical rail (1)    Horizontal rail (2)    Carrier (3)    Mixing plate (4)    Sliding seat. (21)