A method that in the treatment of arsenic contained in a nonferrous smelting intermediary product, especially treatment of copper-arsenic compounds in the form of an intermetallic compound, would produce stable scorodite excelling in filterability easily without cumbersome operation with high reproducibility. Scorodite is produced through the leaching step of leaching out arsenic in the presence of a sulfurizing agent and an oxidizing agent from a nonferrous smelting intermediary product containing copper-arsenic compounds in the form of an intermetallic compound; the liquid adjusting step of adding an oxidizing agent to the leachate to thereby carry out an oxidation from trivalent arsenic to pentavalent arsenic; and the crystallization step of converting the arsenic contained in the adjusted liquid to scorodite crystals.
