TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Process: The organic refuse comprising polysaccharide containing holocellulose (10% or more) is liquefied with a liquefying enzyme before saccharifying in the saccharification and fermentation portion (I). Preferred Compound: The glucoamylase and/or cellulose are used as saccharogenic amylase in production of alcohol.    TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The saccharification and fermentation portion (I) performs saccharification and alcoholic fermentation of organic refuse simultaneously. A portion of mash produced in saccharification and fermentation portion (I) is further subjected to alcoholic fermentation. A portion of mash produced in saccharification and fermentation portion (I) is returned to the beginning of the saccharification and fermentation portion (I). The biogas produced in the fermentation portion (II) is used as an energy source of a distillation portion (12) and a dryer portion (23). Preferred Portion: The yeast is cultured, and supplied to the saccharification and fermentation portion (I) continuously or intermittently by a yeast supply portion. The alcohol production system has a distillation portion which distills the mash produced by the saccharification and fermentation portion (I) into crude alcohol and a distillation residue, a dehydration portion (13) which dehydrates the crude alcohol to obtain alcohol, a fermentation portion (II) which carries out methane fermentation of distillation residue and a dryer portion which dries the slaking residue discharged from the fermentation portion (II). The fermentation portion (II) has a methane-fermentation tank which introduces air, and a water tank. The biogas and air are contacted in the methane-fermentation tank to reduce the concentration of hydrogen sulfide in the biogas. The mixed gas of biogas and air is circulated between the fermentation portion (II) and water tank to air-oxidize hydrogen sulfide, and to set hydrogen sulfide as sulfur or sulfate ion. The concentration of hydrogen sulfide in the mixed gas is further reduced.