A wastewater treatment method for obtaining demanganized wastewater from sulfuric acid acidified wastewater containing aluminum, magnesium, and manganese, wherein, through the following steps to, the demanganized wastewater is obtained in such a manner that, while precipitation of magnesium is controlled, manganese is precipitated and separated: a step of adding an acid or an alkali to sulfuric acid acidified wastewater, the alkali being any one or more of calcium carbonate, slaked lime, sodium hydroxide, potassium hydroxide, an aluminum hydroxide precipitate obtained in a subsequent step, a filtrate obtained in a subsequent step, and demanganized wastewater obtained in a subsequent step, and separating the sulfuric acid acidified wastewater into a dealuminized solution having 0.1 g/L or less of an aluminum concentration and an aluminum hydroxide precipitate represented as [Al 3] by adjusting a pH of the wastewater to be in a range of not less than 4.0 and not more than 5.0; a step of adding a slurrying solution to the aluminum precipitate obtained in the step to form a slurry, and adding an alkali thereto, the alkali being any one or more of calcium carbonate, slaked lime, sodium hydroxide, potassium hydroxide, an aluminum hydroxide precipitate obtained in the step, a filtrate obtained in the step, and demanganized wastewater obtained in the step, to adjust pH to be in a range of not less than 9.0 and not more than 9.5 to stabilize an aluminum hydroxide in the slurry to form a pH-adjusted aluminum precipitate slurry including a stabilized aluminum hydroxide precipitate that has no property of changing into a hydrotalcite-like aluminum compound hydroxide; a step of adding an alkali to the dealuminized solution obtained in the step, the alkali including either an aluminum hydroxide precipitate or a filtrate that are obtained in the step, with 0.1 g/L or less of aluminum concentration in the dealuminized solution, to adjust pH to be in a range of not less than 8.0 and not more than 9.0, and then adding an oxidizing agent to perform oxidation neutralization, whereby an oxidized and neutralized slurry is formed; a step of solid-liquid separating the oxidized and neutralized slurry obtained in the step to separate into a manganese precipitate and demanganized wastewater; and a step of solid-liquid separating the pH-adjusted aluminum precipitate slurry obtained in the step to separate into an aluminum hydroxide precipitate and a filtrate. a step of adding an acid or an alkali to sulfuric acid acidified wastewater, the alkali being any one or more of calcium carbonate, slaked lime, sodium hydroxide, potassium hydroxide, an aluminum hydroxide precipitate obtained in a subsequent step, a filtrate obtained in a subsequent step, and demanganized wastewater obtained in a subsequent step, and separating the sulfuric acid acidified wastewater into a dealuminized solution having 0.1 g/L or less of an aluminum concentration and an aluminum hydroxide precipitate represented as [Al 3] by adjusting a pH of the wastewater to be in a range of not less than 4.0 and not more than 5.0; a step of adding a slurrying solution to the aluminum precipitate obtained in the step to form a slurry, and adding an alkali thereto, the alkali being any one or more of calcium carbonate, slaked lime, sodium hydroxide, potassium hydroxide, an aluminum hydroxide precipitate obtained in the step, a filtrate obtained in the step, and demanganized wastewater obtained in the step, to adjust pH to be in a range of not less than 9.0 and not more than 9.5 to stabilize an aluminum hydroxide in the slurry to form a pH-adjusted aluminum precipitate slurry including a stabilized aluminum hydroxide precipitate that has no property of changing into a hydrotalcite-like aluminum compound hydroxide; a step of adding an alkali to the dealuminized solution obtained in the step, the alkali including either an aluminum hydroxide precipitate or a filtrate that are obtained in the step, with 0.1 g/L or less of aluminum concentration in the dealuminized solution, to adjust pH to be in a range of not less than 8.0 and not more than 9.0, and then adding an oxidizing agent to perform oxidation neutralization, whereby an oxidized and neutralized slurry is formed; a step of solid-liquid separating the oxidized and neutralized slurry obtained in the step to separate into a manganese precipitate and demanganized wastewater; and a step of solid-liquid separating the pH-adjusted aluminum precipitate slurry obtained in the step to separate into an aluminum hydroxide precipitate and a filtrate.