To easily manufacture a concrete plate which is free from any adverse effect to deteriorate its bending strength and facilitates the laying of wiring for light projection and further, the setting of a hole diameter by using a force plunger with plural pins fixed at a specified interval on the lower face and forming plural through holes simultaneously with pressure dehydration molding.

If a hydraulic press ram 8 is lowered, concrete mortar 7 streams through a frame to become a plate. In addition, the press ram 8 is further lowered to press the concrete mortar 7 to form a concrete plate 11. At the same time, pins 10 implanted into a force plunger 9 pierce through the bottom face of the plate 11 from its upper face, and water contained in the mortar 7 permeates through a water drain hole 5 in a drain iron plate 6 and a water drain hole in a bottom force 3 of a molding die to be dehydrated and formed into the concrete plate 11 with holes almost free from moisture. Thus the concrete plate 11 formed as described has through holes 10a formed in recessed strip grooves 4 from the top face to the bottom face.