Anaerobic membrane bioreacter (AnMBR), an combination of methane fermentation and membrane technology, have recently been attracting attention as a creation energy and energy saving wastewater treatment method. AnMBR has not yet been used for treating real sewage because related knowledge is not enough. In this study, long-term continuous treatment experiment of real sewage using AnMBR was conducted to evaluate the treatment performance. Hydraulic retention time (HRT) was shorted stepwise from 24 h to 4 h. As a result, high COD removal efficency (84 to 90%) was obtained in whole experiment. In particular, a high treated water quality with BOD <20 mg / L and COD <60 mg / L was obtained stably at the HRT of 6 to 8 h, which is the typical condition of the conversional activated sludge process. The sludge production yield of An MBR at a HRT of 8h is 0.12 gVSS / gCODrem, which is 1/3 to 1/5 of that for the conversional activated sludge process, and a methane conversion efficiency of influent COD was high as 69.3±3.2 %. A case study comparing the performance between AnMBR and the conversional activated sludge process indicated that the AnMBR would increase the energy recovery efficency by 1.6 times and reduce the excess sludge by half or less.