A fuel production method includes steps of charging livestock excrement into an reaction vessel and charging water whose amount is five times to twenty times as much as the charged livestock excrement, injecting saturated steam having a pressure of ranging from 0.62 MPa to 1.9 MPa into the reaction vessel after the excrement and water are charged, low-molecularizing the excrement by decomposing the organic molecules contained in the livestock excrement, while removing ammonia by stirring inside of the reaction vessel with injecting steam on and stopping stirring when the temperature of a bottom portion in the reaction vessel rises 125 °C or above. An apparatus therefor is provided where ammonia inhibiting methane fermentation of livestock excrement is removed, and increase of methane fermentation rate and gas generation amount can be achieved by decomposing organic compounds such as hydrocarbons, proteins, and fats contained in the livestock excrement into low-molecular weight compounds.
