A method of producing a sugar liquid and a xylooligosaccharide includes Steps (1) to (3): Step (1): hydrolyzing a cellulose-containing biomass with a filamentous fungus-derived cellulase; Step (2): subjecting the hydrolysate of Step (1) to solid-liquid separation, and filtering the solution component through an ultrafiltration membrane to recover cellulase as a non-permeate, and to recover a sugar liquid as a permeate; and Step (3): reacting the recovered cellulase in Step (2) with a xylan-containing material, and recovering a xylooligosaccharide produced, Step (3) being independent from Step (1).