NOVELTY - Two-phase type methane fermentation reactor comprises gate valves between the acid fermentation tank and the methane fermentation tank and between the methane fermentation tank and the settling tank.    USE - For generation of methane gas from organic waste materials e.g. swinery excrements and kitchen garbage which may be used as a fuel gas.    ADVANTAGE - The gate valves allow one way flow of the liquid from the acid fermentation tank, the methane fermentation tank and the settling tank successively in order to preventing troublesome backflow of the liquid. Subsequently, there is no reduction in methanogen concentration, fermentation efficiency, or decrease in activity or dissolution of the methanogen microorganisms compared to the prior art.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a reactor for two-phase type methane fermentation of an organic waste material which comprises:    (1) the acid fermentation tank (1) which receives a feed liquid for fermentation treatment;    (2) the methane fermentation tank (2) of gas holder type positioned side-by-side to (1) where an upper space serves as the methane gas holder (6);    (3) a first vertical partition wall (4) partitioning (1) and (2);    (4) a settling tank (3) positioned side-by-side to (2) from where digestion liquid is discharged;    (5) a second vertical partition wall (5) partitioning (2) and (3);    (6) a first gate valve (4A) positioned on (4) for controlling the liquid flow between (1) and (2);    (7) a second gate valve (5A) positioned on (5) for controlling the liquid flow between (2) and (3); and    (8) a methane gas outlet pipeline (10) having a stopcock valve (10A) connected to (6).    DESCRIPTION OF DRAWING(S) - The figure shows a schematic cross sectional view of the reactor.    acid fermentation tank (1)    methane fermentation tank (2)    settling tank (3)    first partition wall (4)    first gate valve (4A)    second partition wall (5)    second gate valve (5A)    gas holder (6)    methane outlet pipeline (10)    stopcock valve. (10A)