To completely stabilize waste containing heavy metals contained in general and industrial waste by producing a treating agent for waste containing heavy metals by using a hydration product having a specified particle size as a main component.

Fine powder which is obtained by a method in which a cured substance for a building material obtained by adding water and, as required, an additive such as fine aggregate etc., to a hydraulic substance such as cement and curing the mixture is pulverized or ground by an ordinary method and a hydration product which is obtained by a method in which a large amount of water is added to a hydraulic substance, and the mixture is hydrated with heating and stirring, dewatered, and filtered are used as a treating agent for waste containing heavy metals. On this occasion, the hydration product 0.1μm-0.5mm in average particle size is used. The product mainly containing a latent hydraulic substance is preferable, the product mainly containing blast furnace granulation slag is more preferable, and the product obtained by curing a composition mainly containing blast furnace granulation slag, an alkali stimulating agent, and water is especially preferable.