In the case of extruding a W/O type emulsion having a high viscosity obtained by stirring a mixture of a vinyl monomer solution composed of a vinyl monomer which is water insoluble and in a liquid state at normal temperature, a surface active agent having a hydrophilic-lipophylic balance of 3 to 6, and a polymerization catalyst with water, cement, and synthetic fibers through a die, at least one rectifying plate having a given form is disposed in the die near the outlet thereof to direct the synthetic fibers in the W/O type emulsion to the extruding direction.When the tabular plate obtained by extrusion-molding the W/O type emulsion by the method of this invention is hardened and dried, a light-weight and high-strength plastic concrete suitable for building materials is obtained.