An aeration-less water treatment apparatus including an anaerobic reactor which receives sewage to cause the sewage to flow as an upward stream, and an aerobic reactor which receives treated water from the anaerobic reactor to cause the water to flow as a downward stream so that the water contacts aerobic microorganisms and air to aerobically treat the polluted matter in the water, the apparatus further including a suspended sludge section located in a lower part of the anaerobic reactor and in which the anaerobic microorganisms are suspended in the sewage, and a carrier section located in an upper part of the anaerobic reactor and having carriers to which the anaerobic microorganisms are attached, the anaerobic microorganisms having flowed from the suspended sludge section being further attached to the carriers.