A method of producing a sugar solution includes (1) to (3): (1) preparing a slurry of a cellulose-containing biomass pretreated material and an inactivated cellulose, (2) hydrolyzing the slurry in (1) by adding a filamentous fungus-derived cellulase to the slurry, and (3) separating a hydrolysate in (2) into a solution component and a hydrolysis residue through solid-liquid separation, and filtering the solution component through an ultrafiltration membrane, thereby recovering the filamentous fungus-derived cellulase as a non-filtrate and the sugar solution as a filtrate.