There is provided an apparatus for treating a biomass feedstock at a high temperature, including a cooling means for cooling a biomass treated liquid at a high temperature; an enzymatic saccharification tank for saccharifying a cooled treated liquid with an enzyme; a solid-liquid separation apparatus for removing water-slightly soluble substances contained in a saccharide solution taken out from the enzymatic saccharification tank and a foreign substance removing unit provided with a microfiltlation (MF) membrane; a dilution tank, disposed downstream of the foreign substance removing unit, for diluting the saccharide solution from which the water-slightly soluble substances are removed by adding water thereto; a water separation unit, provided with a reverse osmosis (RO) membrane, for removing water from the diluted saccharide solution so as to obtain concentrated saccharide solution.