To provide a novel technique for solving the following problems: because hexavalent chromium having cancer-causing property is eluted when curing reaction of Portland cement and blast furnace cement used as a curing agent is employed for executing solidification treatment of a soft ground, ferrous sulfate has been mixed, but the effect of the mixture is not sufficient.

In the novel technique, ferrous sulfate and one kind of sulfite (sodium sulfite, magnesium sulfite, calcium sulfite) are mixed in Portland cement and blast furnace cement, or one or several kinds of sulfite only are added to control elution of hexavalent chromium. Alternatively, ferrous sulfate and one of sulfites (sodium sulfite, magnesium sulfite, calcium sulfite) are dissolved in water, and the water obtained is used as kneading water for Portland cement and blast furnace cement, or one or several kinds of sulfite only is dissolved in water, and the water prepared is used as kneading water for controlling elution of hexavalent chromium.