NOVELTY - Bio-gas is produced from liquid fertilizer, by heating the liquid fertilizer in a fermenter (5) using heat naturally generated from compost (2) while maturing, or using heat supplied from a hot-air blowing device or electric heater (19,20).    USE - For producing bio-gas (methane) from organic substance such as organic refuse, livestock waste, agricultural residue, in farm house.    ADVANTAGE - The novel bio-gas production method, enables acceleration of bio-gas production from organic substance. The bio-gas producing apparatus enables simultaneous production of solid compost, liquid fertilizer and bio-gas (methane), in farm house, hence improves work efficiency in agricultural field. Since reduced heat resource is utilized, the method is economical. The apparatus provides suitable temperature condition which can be adjusted as required during fermentation. The bio-gas can be produced efficiently in short period using the apparatus. The method and apparatus has high practical value in the production of bio-gas.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is also included for bio-gas production apparatus which is equipped with a compost fermentation field (3), fermenter, a heat conducting unit, and chamber for collecting bio-gas (16), provided to the upper part of the fermenter. The fermenter has a opening (4) for introducing waste and supernatant liquor obtained from the compost fermentation field. The heat conduction part receives heat generated by compost under digestion, from compost fermentation field, and warms liquid fertilizer in the fermenter. The heater and heating unit, such as hot-air blowing in apparatus and external heating apparatus, also warms the liquid fertilizer in the fermenter.    DESCRIPTION OF DRAWING(S) - The figure shows the sectional drawing of the bio-gas production device along A-A line.    Compost (2)    Compost fermentation field (3)    Opening for introduction of waste (4)    Anaerobic fermenter (5)    Liquid fertilizer outlet (9)    Bio-gas outlet (10)    Liquid fertilizer inlet (11)    Heat conduction wall (12)    Chamber for collecting bio-gas (16)    Electric heater (19,20)