Abstract: A high vacuum hot press for producing a multi-layer board. The high vacuum hot press includes a pair of heat insulating members each comprising a heat insulating material and a thin metallic cover defining an evacuated hermetic space accommodating therein the heat insulating material. The heat insulating members are arranged on respective surfaces, facing each other on a pair of bolsters. A pair of hot plates are placed on the heat insulating members, respectively. A multi-layer workpiece is disposed between the hot plates in a sealed space in a sealing unit. The multi-layer work includes wafers and an adhesive base material. The sealed space is evacuated to a high vacuum by an evacuating unit, and the multi-layer workpiece is heated by a heating unit under a high vacuum.