The object is to remove arsenic in a stable form from an arsenic-containing smelting intermediate product. Thus, disclosed is a method for treating an arsenic-containing nonferrous smelting intermediate product, which comprises: a leaching step of subjecting a mixed slurry of a nonferrous smelting intermediate product containing arsenic in the form of a sulfide and a nonferrous smelting intermediate product containing arsenic and metal copper to the oxidation/leaching in an acidic range to produce a leaching solution; a solution preparation step of adding an oxidizing agent to the leaching solution to oxidize trivalent arsenic into pentavalent arsenic, thereby producing a preparation solution; and a crystallization step of converting arsenic contained in the preparation solution into a scorodite crystal.