To provide an inorganic mud transmutation, flocculation and purification treating agent for contaminated drainage to aim at the adsorption/absorption/flocculation separation of contaminant in the purification of the contaminated drainage regardless of inorganic base/organic base, the solidification/immobilization of metals (including heavy metals) to prevent the elution and the transmutation to soil near to natural soil in the mud transmutation of separated sludge by the flocculation.

The inorganic based mud transmutation, flocculation and purification treating agent for the contaminated drainage regardless of inorganic base or organic base is constituted so as to blend sodium thiosulfate, calcium chloride, aluminum sulfate and an alkali metal carbonate as essential ingredients with a main component consisting of a natural mineral containing alumina-silicate mainly, iron oxide, soil bacteria and an organic flocculant.