NOVELTY - Methanation (M1), comprises producing methane by culturing methane producing microorganisms using heat processed seaweed that has been made into a substrate after lowering the molecular structure and viscosity of polysaccharide by heat-processing the seaweed.    USE - (M1) Is useful for producing methane, for generating fuel from sewage using the heat energy obtained by (M1) or (I), and for converting into electrical energy (claimed).    ADVANTAGE - (M1) Enables generation of a large amount of gas from seaweed, and to obtain fertilizer as a by product.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following:    (1) methanation apparatus (I), comprising a unit for crushing seaweed, a heating unit, a tank for heat-processing seaweed, and a methane-fermentation tank for producing methane with methane producing microorganisms from the heat-processed sea weed;    (2) a processing method (M2) of seaweed, comprising producing methane by culturing a methane producing microorganism using heat processed seaweed that has been made into a substrate after lowering the molecular structure and viscosity of polysaccharide by heat-processing the seaweed;    (3) lowering the structure and viscosity of polysaccharide of seaweed, by heat-processing the seaweed;    (4) manufacturing a seaweed having low molecule and decreased viscosity polysaccharide, comprising lowering the molecular structure and viscosity of polysaccharide by heat-processing the seaweed;    (5) seaweed having a low molecular structure and decreased viscosity polysaccharide by heat-processing, and obtained by (M2);    (6) seaweed residue obtained from the methane fermentation tank by (M1); and    (7) Bacillus cereus 0Z-6 strain having accession number FERM AP-20381, and Lactobacillus sp. 0Z-7 strain having accession number FERM AP-20382.    DESCRIPTION OF DRAWING(S) - The figure shows an apparatus of the methanation method. (Drawing includes non-English language text).    sewage gas (3)    heat processing tank (12)    microorganism treatment tank (13)    methane fermentation tank (14)    autoclave (21)