A method and apparatus for treating heavy-metal-containing wastewater using a sulfidizing agent. Sulfidizing treatment is carried out by adding a sulfidizing agent to heavy-metal-containing wastewater, while detecting hydrogen sulfide gas generated from the wastewater, such as to maintain a state in which hydrogen sulfide gas is just starting to be generated from the wastewater. When separately recovering each of a plurality of metals from wastewater in which are mixed ions of the plurality of metals, there is repeated for each of the metals a process in which the acidity of the wastewater is adjusted to within a range suitable for the metal to be separated out and recovered, a sulfidizing reaction is carried out on that metal, and the metal sulfide produced is precipitated and filtered off.