To safely and simply treat without generating a harmful gas by consisting the subject agent essentially of an amine derivative or its salt having a structure expressed by a specific formula in the molecule.

This heavy metal-containing waste treating agent is formed by consisting essentially of the amine derivative or its salt having at least one structure expressed by the formula in the molecule. In the formula, each of R1 and R2 represents hydrogen or a hydrocarbon group and both can be the same as or different from each other. M represents one kind of a element or a molecule selected from a group composed of hydrogen, an alkali metal, an alkaline earth metal and ammonium, and lithium, sodium and the like are exemplished. (n) represents an integer of 1-20. When (n) exceeds 20, the solubility of the amine derivative or its salt in water is undesirable lowered. Now, each of R1 and R2 is preferably hydrogen or the 1-20C hydrocarbon group in the view point of the easiness in handling. By the constitution, the heavy metal- containing waste is treated without generating the harmful gas such as H2S, CS2, COS.