NOVELTY - A pressurized liquid/solid organic substance is injected to a solubilized tower (1) with oxygen at 0.5 times less than the theoretical amount. The solubilized gas-liquid is circulated to a methanation reactor (15) in the presence of a catalyst. The gas from the reactor is decarbonized by passing alkali.    USE - For generating synthetic natural gas (SNG) from e.g. solid/liquid organic substances or biomass.    ADVANTAGE - Reduces manufacturing cost by transforming solid/liquid organic substance to heating gas. As solubilized tower outlet product is released by liquid-gas phase, the presence of harmful component is not observed substantially. By decarbonizing acids of carbon dioxide by alkali, occurrence of corrosion, crack, etc., can be suppressed. Environmental pollution can be reduced remarkably by using non-toxic substance.    DETAILED DESCRIPTION - The valves of the injection apparatus are operated and solid waste is charged to an injection apparatus (100) at normal pressure. The pressure in the injection apparatus is increased corresponding to the solubilized tower and pressurized liquid organic substance or slurry such as organic compounds containing liquid, solid organic substance grinding body with water are circulated in the tower. The temperature of the solubilized tower is maintained at 374 degrees C or more, and the pressure is maintained greater than 22 MPa-G. The sludge and/or the metal components are removed. The liquid-gas mixture is obtained from the tower. The remaining mixture containing 5-20 times of relative liquid amount, is circulated to methanation reactor in the presence of active catalyst. The catalyst is carried by a support, such that the load of the active ingredients is 0.01-10% of support. Heat energy or power energy is recovered from the gaseous phase.    DESCRIPTION OF DRAWING(S) - The figure shows the flow-sheet of heating gas manufacturing method.    Solubilized tower (1)    Methanation reactor (15)    Injection apparatus (100)