An apparatus for advanced wastewater treatment using up & down aerobic-anaerobic reactors of channel type in the single reaction tank provides the effluent recycle of channel type aeration reactor (internal cycle). For this, the anaerobic reactor of channel type is under the aerobic reactor of channel type in the single reaction tank. And the flow of the wastewater in the single reaction tank is based on the water level difference between inlet and outlet, and the air lift effect of the air diffusers. The partitions of channel type anaerobic reactor and the partitions of channel type aerobic reactor are cross each other. Consequently, the energy cost is cut down because the wastewater flow does not need much pumping energy. And the site need is reduced because of up & down aerobic-anaerobic reactors of channel type in the single reaction tank.