NOVELTY - The system (10A) has a hydrothermal decomposition process unit (17) which decomposes biomass feedstock (11) having cellulose, hemicellulose, and lignin on high temperature and voltage conditions, and removes lignin component and hemicellulose component by processing tank which includes gas-liquid interface. A discharge liquid introduction line (L2) introduces hot-water discharge liquid containing biomass hot water solubles to slurrying tank (21), and mixes biomass solid content (20) with discharge liquid to make mixture slurry.    USE - Processing system of biomass feedstock for manufacturing sugar liquid used for manufacture of alcohol (all claimed).    ADVANTAGE - Since the discharge liquid introduction line introduces hot-water discharge liquid containing biomass hot water solubles to slurrying tank, the introduction amount of the water at the time of carrying out the slurrying process is reduced and the improvement of plant processing efficiency can be achieved. The biomass solid content is injected in liquid so that the reaction stop can be efficiently performed by cooling biomass solid content by heat exchange with liquid directly and acid and alkali are diluted. Hence the excessive decomposition of the residual hemicellulose entrained to biomass solid content, residual lignin, and main component cellulose is suppressed and the improvement of the recovery for cellulose can be achieved while suppressing generation of reaction inhibition component.    DETAILED DESCRIPTION - The system has biomass solid content extraction unit (18) that extracts biomass solid content that is hot-water non-soluble component. A filter is arranged on discharge liquid introduction line. A cooling element is located on discharge liquid introduction line. A saccharification tank saccharifies mixture slurry slurried by slurrying tank. A solid-liquid separator separates solid portion from sugar liquid after saccharifying by saccharification tank. A moisture-content separation apparatus removes water from sugar liquid after solid separation. Rehydaration line returns water separated from moisture-content separation apparatus to slurrying tank. The biological treatment apparatus is set on rehydaration line. INDEPENDENT CLAIMS are included for the following:    (1) a sugar liquid production method involves removing impurity in discharge liquid discharged from hydrothermal decomposition process unit; and    (2) an alcohol manufacturing method involves performing alcoholic fermentation using the sugar liquid obtained by the sugar liquid production process using biomass feedstock.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the processing system of the biomass. (Drawing includes non-English language text)    Processing system (10A)    Biomass feedstock (11)    Hydrothermal decomposition process unit (17)    Biomass solid content extraction unit (18)    Biomass solid content (20)    Slurrying tank (21)    Discharge liquid introduction line (L2)