A molding machine for the production of polygonal structural elements, e.g. concrete squares, comprises an assembly of vertical plates disposed between a pair of end members of a support and defining generally flat mold cavities of the shape desired with respective bottom members and lateral gates. The lateral gates are hinged to the rectangular bottom members at the ends thereof and are interconnected by respective bars so that all of the lateral gates along each side of molded cavities can be swung outward into release position and indeed into mold-closing positions by laterally shiftable carriers on the end members of the support.
