CLAIMS 1. A method for producing a cyanohydrin, comprising allowing a carbonyl compound to react with prussic acid in a buffer solution having a pH of less than 7 to obtain the cyanohydrin. 5 2. A method for producing a cyanohydrin, comprising adding prussic acid to a buffer solution containing a carbonyl compound and having a pH of less than 7, and being held in a predetermined temperature range, to allow the carbonyl compound to react with the prussic acid in the buffer solution to thereby obtain the cyanohydrin. 3. 10 The method according to claim 1 or 2, wherein the buffer solution comprises a weak acid and a salt of the weak acid. 4. The method according to any one of claims 1 to 3, wherein the buffer solution comprises an organic acid and a salt of the organic acid. 5. The method according to claim 4, wherein the organic acid is the same - hydroxycarboxylic acid as an -hydroxycarboxylic acid produced when the 15 cyanohydrin is hydrolyzed. 6. The method according to claim 4, wherein the organic acid is glycolic acid. 7. The method according to any one of claims 1 to 6, wherein the carbonyl compound is an aldehyde. 8. 20 The method according to any one of claims 1 to 7, wherein the carbonyl compound is formaldehyde. 1