The present invention intends to provide a practically valuable insolubilizing material for a designated hazardous substance (a heavy metal or the like) and an insolubilization method using the insolubilizing material for a designated hazardous substance, the insolubilizing material and method: making it possible to conduct treatment in a neutral region from start to finish to effectively insolubilize and immobilize a heavy metal or the like, which is contained in soil and the vicinity of the surface of the soil and which has adverse effects on health, by adding the insolubilizing material to the soil to mix with the soil, or spraying the insolubilizing material on the soil; and making the treated matter reusable, environmentally friendly, and neutral without fail. In order to achieve the purpose, the present invention provides an insolubilizing material for a designated hazardous substance, making it possible to conduct treatment to soil so that the soil does not reach a strongly basic region of a pH of 11 o
