We Claim:
1. A method for producing a sugar liquid using a cellulose-containing biomass as a raw
material, said method comprising:
(1) hydrolyzing a cellulose-containing biomass to produce an aqueous sugar solution; and
(2) filtering the obtained aqueous sugar solution through a reverse osmosis membrane to collect a purified sugar liquid from the feed side, while removing fermentation-inhibiting substances from the permeate side.

2. The method for producing a sugar liquid according to claim 1, wherein the pH of said aqueous sugar solution in Step (2) is adjusted to 1 to 5.
3. The method for producing a sugar liquid according to claim 2, wherein the pH of said aqueous sugar solution in Step (2) is adjusted to 1 to 3.
4. The method for producing a sugar liquid according to any one of claims 1 to 3, wherein said fermentation-inhibiting substances comprise one or more selected from the group consisting of organic acids, furan compounds and phenolic compounds.
5. The method for producing a sugar liquid according to claim 4, wherein said organic acid is formic acid or acetic acid.
6. The method for producing a sugar liquid according to claim 4, wherein said furan compound is hydroxymethylfurfural or furfural.
7. The method for producing a sugar liquid according to claim 4, wherein said phenolic compound is vanillin, acetovanillin or syringic acid.
8. The method for producing a sugar liquid according to any one of claims 1 to 7, wherein said purified sugar liquid in said Step (2) is a sugar liquid containing a monosaccharide as a major component.
9. The method for producing a sugar liquid according to any one of claims 1 to 8,

wherein said aqueous sugar solution obtained in said Step (1) is further filtered through a microfiltration membrane and/or ultrafiltration membrane to remove fine particles and macromolecular components before the treatment of Step (2).
10. The method for producing a sugar liquid according to any one of claims 1 to 9, wherein the temperature of said aqueous sugar solution in Step (2) is adjusted to 40 to 80°C.
11. The method for producing a sugar liquid according to any one of claims 1 to 10, wherein said Step (2) is a step of filtering said aqueous sugar solution through a nanofiltration membrane and filtering the obtained filtrate through said reverse osmosis membrane.
12. The method for producing a sugar liquid according to any one of claims 1 to 11, wherein functional layer(s) of said reverse osmosis membrane in Step (2) is/are polyamide.
13. The method for producing a sugar liquid according to any one of claims 1 to 11, wherein functional layer(s) of said reverse osmosis membrane in Step (2) is/are cellulose acetate.
14. A method for producing a sugar liquid according to any one of claims 1 to 13, further comprising the step of fermenting the sugar liquid obtained from Step (2) for producing a chemical product.