To provide a cement solidifying material which contains a harmful matter-reducing material having the capacity of reducing anionic hexavalent chromium, and the performance of reducing cationic harmful heavy metals, and to provide a method for reducing harmful matters using the same.

The solidifying material contains desulfurization slag, a cation sorption material, and a hydraulic material. In the method for reducing the harmful matters, the same solidifying material is used. By the grain sizes of the desulfurization slag powder, the reduction effect on hexavalent chromium can be expected in both of immediate efficacy and delayed efficacy. By using the solidifying material, simultaneously with solidifying treatment to industrial waste such as garbage incineration ashes, sludge incineration ashes, collected dust of these ashes, weak soil, sludge, construction waste soil and molten slag, cadmium, lead, trivalent chromium, and hexavalent chromium are reduced, and the outflow of harmful matters can be suppressed.