an injection unit is disclosed with bridges for the plastification cylinder and for the plastification screw , which bridges are movable on fixed guide rods . there is a central injection cylinder and drive cylinders located diametrically with respect thereto . the pistons of the drive cylinders are firmly seated on the guide rods . a support device supports the injection unit on the machine pedestal of the plastic injection molding machine . the support device includes a fixed support , a movable support , and an elevation adjuster which transmits the supported load . the movable support is fastened to at least one of the bridges . with such an arrangement , bending of the support rods is virtually prevented during an injection operation .