A method of producing a sugar liquid from a cellulose-containing biomass includes (1) hydrolyzing a cellulose-containing biomass using a filamentous fungus-derived cellulose and carrying out solid-liquid separation into a sugar liquid and a hydrolysis residue; (2) washing the hydrolysis residue in (1) using an aqueous alkaline solution and an aqueous inorganic salt solution independently and recovering, as a washing liquid, the filamentous fungus-derived cellulase adsorbed to the hydrolysis residue; and (3) filtering the washing liquid in (2) through an ultrafiltration membrane to recover a sugar liquid as a permeate and the filamentous fungus-derived cellulase as a non-permeate.