PURPOSE: To produce efficiently a high-quality board material, by pressurizing uniformly slurry without having density irregularity.

CONSTITUTION: The title device is provided with a molding chamber 1 into which slurry is filled, a slide surface plate 2 dehydrating the slurry by pressurizing the same, a plurality of cylinders controlling pressing force of the slide surface plate 2 pressing the slurry and a thickness sensor 5 detecting a thickness of the slurry of the molding chamber 1 at a plurality of points. A vibrating valve giving a fine vibration to the slide surface plate 2 is connected with the cylinder. With this construction, since a thick part of the slurry is vibrated and pressed strongly, solid content is shifted smooth to a thin part through the slurry of the thick part and scattered uniformly.