NOVELTY - An anaerobic-treatment apparatus of organic wastewater comprises wastewater adjustment tank and methane fermentation tank (2) consisting of inflow part of to-be-processed water equipped with water quality survey meter which measures pH, M-alkalinity, and organic acid concentration, outflow part of treated water, biogas outflow part which is equipped with measurement meter of carbon-dioxide-gas (CO2) concentration and is based on measured value from water quality survey meter and concentration measurement meter, and control apparatus which controls M-alkalinity regulator addition amount.    USE - An anaerobic-treatment apparatus of organic wastewater (claimed).    ADVANTAGE - The pH in methane fermentation tank is stored in appropriate range, and high load and removal rate can be maintained.    DETAILED DESCRIPTION - An anaerobic-treatment apparatus of organic wastewater comprises wastewater adjustment tank and methane fermentation tank (2) consisting of inflow part of to-be-processed water equipped with water quality survey meter which measures pH, M-alkalinity, and organic acid concentration, outflow part of treated water, biogas outflow part which is equipped with measurement meter of carbon-dioxide-gas (CO2) concentration and is based on measured value from water quality survey meter and concentration measurement meter, control apparatus which controls M-alkalinity regulator addition amount, and addition apparatus which adds M-alkalinity regulator to to-be-processed water inflow part based on signal from control apparatus. Anaerobic-treatment apparatus processes greater than or equal to 60% alcohol component and SS processes less than or equal to 1% of organic wastewater in conversion of CODcr with respect to all the CODcr of wastewater.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of an anaerobic-treatment apparatus. (Drawing includes non-English language text).    Preparation tank (1)    Methane fermentation tank (2)    Treated-water tank (3)    GSS (4)    Raw water (5)