NOVELTY - Methane fermentation treatment apparatus comprises first electric conductivity detector (21), methane fermentation tank, first flow volume detector (20), second flow volume detector (23), second electric conductivity detector (22), calculating unit (31), base conductivity calculating unit (41) and target dilution water flow rate set unit.    USE - Methane fermentation treatment apparatus for producing biogas by processing organic waste such as dust, excrements, organic refuse and food-processing dreg.    ADVANTAGE - Electric conductivity from ammonia concentration is measured with high precision, thus has high fermentation efficiency.    DETAILED DESCRIPTION - Methane fermentation treatment apparatus comprises first electric conductivity detector (21) which detect electric conductivity of a slurried organic waste supplied to a methane fermentation tank, first flow volume detector (20) which detects the flow volume of the organic waste and second flow volume detector (23) which detects flow volume of a dilution water supplied to the treatment tank, second electric conductivity detector (22) which detects the electric conductivity of the fermented liquor stored in the methane fermentation tank, calculating unit (31) which calculates the dilution-water flow volume, base conductivity calculating unit (41) which calculates the base electric conductivity equivalent to the salt concentration of the fermented liquor, and target dilution water flow rate set unit (42) which set a target value of dilution water flow volume based on target electric conductivity corresponding to a predetermined target ammonia concentration.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the methane fermentation apparatus. (Drawing includes non-English language text).    First flow volume detector (20)    First electric conductivity detector (21)    Second electric conductivity detector (22)    Second flow volume detector (23)    Calculating unit (31)    Base conductivity calculating unit (41)