Method of producing sugar solution

A method of producing a sugar liquid comprising:

• a step of filtering a saccharified liquid obtained by at least one selected from the group consisting of a) enzymatic saccharification of a cellulose-containing biomass pretreated by steam explosion treatment, b) hydrothermal treatment, c) acid treatment, d) alkali treatment, and e) ammonia treatment, through a nanofiltration membrane and a reverse osmosis membrane;
• and
• a two-step washing step consisting of washing said nanofiltration membrane and said reverse osmosis membrane after said filtration, with nitric acid and then with an alkali washing liquid.

A method of producing a sugar liquid comprising:

• a step of filtering a saccharified liquid obtained by at least one selected from the group consisting of a) enzymatic saccharification of a cellulose-containing biomass pretreated by steam explosion treatment, b) hydrothermal treatment, c) acid treatment, d) alkali treatment, and e) ammonia treatment, through a nanofiltration membrane and a reverse osmosis membrane;
• and
• a two-step washing step consisting of washing said nanofiltration membrane after said filtration, with nitric acid and then with an alkali washing liquid.