To provide a composition for quickly and effectively hardening cement, capable of directly mixing with cement or cement-based solidifying materials, for easily forming high-strength solidified body to unsolidified materials containing 2 mass% or more organic components at low cost.

The cement hardening compositions comprise (A) liquids extracted from clay minerals containing huminic acids as main components, (B) inorganic salts, and (C) acid components as reaction accelerators. The cement-based solidifying materials are obtained by mixing cement powder of 100-1000 pts.wt. to the above cement hardening compositions of 100 pts.wt. The cement-based solidifying materials of at least 2 pts.vol. is uniformly scattered on soils of 100 pts.vol. and mixed and aged with the soils for base construction.