Abstract: A method of compression-molding a slurry of a hydraulic inorganic material such as cement or slag, a light-weight aggregate, a reinforced fiber material and other filler material kneaded with water so as to manufacture an inorganic molded product. The slurry is put into a molding frame having a filtering cloth placed over the bottom surface thereof and is then compression-molded in the molding frame by using a molding die while it is suction-dehydrated from on both sides of the molding die surface and the filtering cloth surface. The molding die has a number of vent holes for sucking-dehydration each of which vent holes comprises a small-diameter hole and a large-diameter hole continuous therewith.