An automatic packaging machine including a folding assembly of a continuous sheet of packaging material, in particular paper, having a sliding plane for conveying the continuous sheet of packaging material along a conveying direction is disclosed. The sliding plane includes an entrance end for entering the continuous sheet of paper and two opposite sides parallel to the conveying direction. Further, the folding assembly includes a feeding assembly for feeding the continuous sheet of packaging material along a feeding plane which is substantially orthogonal to the conveying direction and defined at the entrance end of the sliding plane. The folding assembly further includes a block associated with at least one of the opposite sides of the sliding plane and a body associated with the block and provided with a cone-sector surface which supports a longitudinal flap during longitudinal creasing and accompanies it during the folding along the longitudinal creasing.