As means for producing a biodiesel oil from a feed oil containing a free fatty acid at high efficiency, the following processes (1) to (3) are provided: (1) a process for producing a higher fatty acid ester, comprising reacting a lower alcohol with a higher fatty acid in the presence of an amorphous carbon having a sulfonate group introduced therein, thereby producing the higher fatty acid ester; (2) a process for producing a higher fatty acid ester, comprising reacting a lower alcohol with a higher fatty acid and a higher fatty acid triglyceride in the presence of an amorphous carbon having a sulfonate group introduced therein, thereby producing the higher fatty acid ester by both of the reaction between the lower alcohol and the higher fatty acid and the reaction between the lower alcohol and the higher fatty acid triglyceride; and (3) a process for producing a higher fatty acid ester, comprising: reacting a lower alcohol with a higher fatty acid and a higher fatty acid triglyceride in the presence of an amorphous carbon having a sulfonate group introduced therein, thereby producing the higher fatty acid ester by both of the reaction between the lower alcohol and the higher fatty acid and the reaction between the lower alcohol and the higher fatty acid triglyceride; and reacting the unreacted lower alcohol with the unreacted higher fatty acid triglyceride in the presence of an alkali hydroxide, thereby producing the higher fatty acid ester.