PURPOSE: To ensure high strength and various functions by incorporating a specified part and parts formed with a hydraulic material or a material contg. the hydraulic material and different from the specified part in microstructure.

CONSTITUTION: An org. porous substrate such as plastic foam, e.g. soft polyurethane foam is impregnated with a hydraulic slurry of cement, etc., and dried to obtain a hydraulic porous structure consisting of a three-dimensional skeleton 1 and three-dimensional open pores 2 formed with the hydraulic material or a material contg. the hydraulic material and different from the skeleton 1 in microstructure. This porous structure has 10μm to 50mm pore diameter and 50-95% porosity. The porous structure is then immersed in a hydraulic slurry of cement, etc., under reduced pressure while removing bubbles, the pores 2 are filled with the slurry and this slurry 2 is hardened to produce the objective hydraulic composite structure.