NOVELTY - Volatile organic acid is added to cellulose biomass (A) slurry, primary saccharification decomposition of hemicellulose contained in cellulose biomass slurry is carried out, sccharified to 5C pentasaccharide, primary solid-liquid-separation process is carried out, sulfuric acid is added, collected, and water (C) is added to dehydrate cake (U), to obtain slurry. Secondary saccharification decomposition of cellulose contained in obtained slurry is carried out, separated into solid and liquid, alcohol fermentation (P) processed, distilled (Q), and concentrated, to obtain ethanol.    USE - Manufacture of ethanol used for decomposing cellulose biomass.    ADVANTAGE - The ethanol is economically and efficiently manufactured.    DETAILED DESCRIPTION - Volatile organic acid is added to a slurry of cellulose biomass, subjected to hydrothermal-treating by a supercritical state or a subcritical state, primary saccharification decomposition of hemicellulose contained in the cellulose biomass slurry is carried out and sccharified to 5C pentasaccharide, and a primary solid-liquid-separation process is carried out for separating the slurry into solid and liquid. Sulfuric acid is added to the obtained 5C saccharified liquid, collection process is carried out by air-stripping-process or distillation process to collect the volatile organic acid contained in the 5C saccharified liquid, and water is added to the collected dehydrated cake, to obtain slurry. Secondary saccharification decomposition of cellulose contained in the obtained slurry is carried out by hydrothermal-process in a supercritical state or a subcritical state, saccharified to 6C saccharides, secondary solid-liquid-separation process is carried out to separate the slurry into solid and liquid, the obtained 5C saccharified liquid and 6C saccharide liquid are subjected to fermentation process in which alcoholic fermentation of 5C saccharified liquid and 6C saccharide liquid is carried out, the obtained ethanol fermented liquor is distilled and ethanol is concentrated, to obtain ethanol. The collected volatile organic acid is recycled, and one or more portion of recycled volatile organic acid is added to the slurry during the primary saccharification decomposition process.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow chart explaining manufacture of ethanol. (Drawing includes non-English language text)    Cellulose biomass (A)    Water (C)    Alcohol fermentation (P)    Distillation (Q)    Dehydrated cake (U)