An apparatus for treating a biomass feedstock at a high temperature, includes a cooling device 90 for cooling a biomass treated liquid at a high temperature; an enzymatic saccharification tank 103 for saccharifying a cooled treated liquid 101B with an enzyme; a solid-liquid separation apparatus 112 for removing water-slightly soluble substances contained in a saccharide solution 104 taken out from the enzymatic saccharification tank 103 and a foreign substance removing unit 113 provided with a microfiltration (MF) membrane 113a; a dilution tank 132, disposed downstream of the foreign substance removing unit 113, for diluting the saccharide solution from which the water-slightly soluble substances are removed by adding water thereto; a water separation unit 116, provided with a reverse osmosis (RO) membrane 116a, for removing water 114 from the diluted saccharide solution so as to obtain concentrated saccharide solution 115.