To provide a suitable, e.g. simpler, method and a system for manufacturing a treated product of a harmful substance which and a product containing harmful substances made more harmless.

The method comprises supplying an agglomeration of a treatment target harmful metal from a feeder 11 to a reaction vessel 10, supplying a thermosetting resin to the reaction vessel 10 through a feeder 15 and starting to mix and agitate the thermosetting resin with the harmful metal. The agglomeration of the harmful metal, a reaction inhibitor, unslaked lime, scavenger and water are supplied according to the requirement from feeders 12 to 16 while continuing the mixing agitation, and a thermosetting process of allowing the thermosetting resin to thermoset is carried out in order to manufacture a treated product of the harmful material. A material containing the treated product of the harmful material within it is also provided.