A method for producing dihydroxyindoles, comprising: a step 1 of obtaining an aqueous first solution including dihydroxyindoles obtained by causing at least a material selected from the group consisting of 3-(3,4-dihydroxyphenyl)alanine and a derivative of 3-(3,4-dihydroxyphenyl)alanine to react with hexacyanoferrate; a step 2 of obtaining an oleaginous second solution in which the dihydroxyindoles are extracted in an extraction solvent by mixing the first solution obtained in the step 1 with the extraction solvent; wherein the extraction solvent includes an organic solvent whose octanol/water distribution coefficient is 0 or more and 4.0 or less; and a step 3 of obtaining an aqueous third solution by evaporating the extraction solvent from a mixture of the second solution obtained in the step 2 and water, wherein the dihydroxyindoles are extracted in a tank A in the step 2, the second solution is discharged from the tank A, the second solution is supplied to a tank B, and then the step 3 is performed in the tank B; wherein the derivative of 3-(3,4-dihydroxyphenyl)alanine includes one or more of 3,4-dihydroxy-D-phenylalanine, 3,4-dihydroxy-L-phenylalanine, N-octanoyl-4-(2-aminoethyl)benzene-1,2-diol, N-octanoyl-4,2-(3,4-dihydropheny)ethylamine, 4-(2-aminoethyl)benzene-1,2-diol, potassium salt and sodium salt of 3,4-dihydroxy-D-phenylalanine, potassium salt and sodium salt of 3,4-dihydroxy-L-phenylalanine, lower alkyl esterof 3-(3,4-dihydroxyphenyl)alanine having a carbon number of 1 to 4, α-lower alkyl 3-(3,4-dihydroxyphenyl)alanine having a carbon number of 1 or more and 4 or less, and isomers thereof. a step 1 of obtaining an aqueous first solution including dihydroxyindoles obtained by causing at least a material selected from the group consisting of 3-(3,4-dihydroxyphenyl)alanine and a derivative of 3-(3,4-dihydroxyphenyl)alanine to react with hexacyanoferrate; a step 2 of obtaining an oleaginous second solution in which the dihydroxyindoles are extracted in an extraction solvent by mixing the first solution obtained in the step 1 with the extraction solvent; wherein the extraction solvent includes an organic solvent whose octanol/water distribution coefficient is 0 or more and 4.0 or less; and a step 3 of obtaining an aqueous third solution by evaporating the extraction solvent from a mixture of the second solution obtained in the step 2 and water, wherein the dihydroxyindoles are extracted in a tank A in the step 2, the second solution is discharged from the tank A, the second solution is supplied to a tank B, and then the step 3 is performed in the tank B; wherein the derivative of 3-(3,4-dihydroxyphenyl)alanine includes one or more of 3,4-dihydroxy-D-phenylalanine, 3,4-dihydroxy-L-phenylalanine, N-octanoyl-4-(2-aminoethyl)benzene-1,2-diol, N-octanoyl-4,2-(3,4-dihydropheny)ethylamine, 4-(2-aminoethyl)benzene-1,2-diol, potassium salt and sodium salt of 3,4-dihydroxy-D-phenylalanine, potassium salt and sodium salt of 3,4-dihydroxy-L-phenylalanine, lower alkyl esterof 3-(3,4-dihydroxyphenyl)alanine having a carbon number of 1 to 4, α-lower alkyl 3-(3,4-dihydroxyphenyl)alanine having a carbon number of 1 or more and 4 or less, and isomers thereof.