To provide an apparatus for treating wastewater containing gallium which can completely and efficiently recover the gallium, a valuable rare element, by treating the wastewater discharged from a compound-semiconductor wafer production factory, a device production factory, etc.

The apparatus has a plurality of gallium adsorption means connected in series. After the wastewater containing gallium is passed through the means connected in series, the means of the first step is separated, and a new gallium adsorption means is connected to the means of the last step.