NOVELTY - Anaerobic-digestion-treatment method of organic wastewater (1) involves separating organic wastewater containing solid content into low suspended solid wastewater (3) and high suspended solid wastewater (10), carrying out anaerobic digestion process (A) to low suspended solid wastewater and anaerobic digestion process (B) to high suspended solid wastewater, immobilizing anaerobic bacteria, performing membrane separation process to separate the effluent (6) of anaerobic digestion process (A), and supplying portion of salt concentrated water to anaerobic digestion process (B).    USE - Anaerobic-digestion-treatment method of organic wastewater e.g. fermentation wastewater and foodstuff-type industrial wastewater.    ADVANTAGE - The organic wastewater is efficiently and reliably treated by anaerobic-digestion-treatment method with long term-stability even when the organic loading is high.    DETAILED DESCRIPTION - Anaerobic-digestion-treatment method of organic wastewater involves separating organic wastewater containing solid content into low suspended solid wastewater having low solid content concentration and high suspended solid wastewater having high solid content concentration, carrying out anaerobic digestion process (A) to low suspended solid wastewater and anaerobic digestion process (B) to high suspended solid wastewater, immobilizing anaerobic bacteria, performing membrane separation process to separate the effluent of anaerobic digestion process (A) with permeated water (17) and salt concentrated water (11) using a membrane which can concentrate salts, and supplying portion(s) of salt concentrated water obtained from the membrane separation process to the anaerobic digestion process (B). An INDEPENDENT CLAIM is included for anaerobic digester of organic wastewater.    DESCRIPTION OF DRAWING(S) - The drawing shows a flowchart explaining anaerobic-digestion-treatment method of organic wastewater.    Organic wastewater (1)    Solid-liquid separator (2)    Low suspended solid wastewater (3)    Effluent (6)    High suspended solid wastewater (10)    Salts concentrated water (11)    Chemical agent (16)    Permeated water (17)