To provide a wastewater treatment apparatus which combines a ditch of an oxidation ditch method and an anaerobic treatment means to remove organic matter, nitrogen, and phosphorus in raw water and to provide a method.

The wastewater treatment apparatus comprises an endless water passage (a ditch 11) which includes an aerobic zone 14 and an anoxic zone 15 and the ditch 11 which controls an oxygen supply means (an aeration device 13) and a circulation flow generation means (an underwater propeller 12) from the upstream side dissolved oxygen concentration and downstream side dissolved oxygen concentration of the aerobic zone 14, the anaerobic means (an anaerobic tank 19) installed in a raw water inflow passage 18 for making the raw water flow into the ditch 11, a solid-liquid separation means (a final settling basin 17) for performing the solid-liquid separation of treated liquid treated in the ditch 11, and a return sludge passage 21 for returning sludge separated by the solid-liquid separation means 17 to the anaerobic tank 19 to mix the sludge with the raw water.