An electrochemical reduction device comprising: an organic material storage tank that stores an organic liquid including an aromatic compound, wherein the aromatic compound is an aromatic hydrocarbon compound or a nitrogen-containing heterocyclic aromatic compound selected from the group consisting of benzene, naphthalene, anthracene, diphenylethane, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, N-alkyldibenzopyrrole, 1 to 4 hydrogen atoms of an aromatic ring of the aromatic hydrocarbon or nitrogen-containing heterocyclic aromatic compound being substituted by an alkyl group having 1 to 6 carbon atoms; an electrode unit including an electrolyte membrane having ionic conductivity, a reduction electrode that is provided on one side of the electrolyte membrane and that contains a reduction catalyst for hydrogenating at least one benzene ring of the aromatic compound, and an oxygen evolving electrode that is provided on the other side of the electrolyte membrane; a power control unit for applying a voltage Va between the reduction electrode and the oxygen evolving electrode; wherein the electrochemical reduction device is further characterized by a circulation pathway that connects the organic material storage tank and the reduction electrode of the electrode unit, the organic liquid passing through the circulation pathway; a concentration measurement unit for measuring a concentration of the aromatic compound to be supplied to the reduction electrode; and a raw material supply amount adjustment unit for adjusting the amount of the organic liquid including the aromatic compound to be supplied to the reduction electrode per unit time based on the concentration of the aromatic compound measured by the concentration measurement unit, wherein the raw material supply amount adjustment unit is configured to increase the amount of the organic liquid to be supplied to the reduction electrode when the concentration of the aromatic compound is decreased. an organic material storage tank that stores an organic liquid including an aromatic compound, wherein the aromatic compound is an aromatic hydrocarbon compound or a nitrogen-containing heterocyclic aromatic compound selected from the group consisting of benzene, naphthalene, anthracene, diphenylethane, pyridine, pyrimidine, pyrazine, quinoline, isoquinoline, N-alkylpyrrole, N-alkylindole, N-alkyldibenzopyrrole, 1 to 4 hydrogen atoms of an aromatic ring of the aromatic hydrocarbon or nitrogen-containing heterocyclic aromatic compound being substituted by an alkyl group having 1 to 6 carbon atoms; an electrode unit including an electrolyte membrane having ionic conductivity, a reduction electrode that is provided on one side of the electrolyte membrane and that contains a reduction catalyst for hydrogenating at least one benzene ring of the aromatic compound, and an oxygen evolving electrode that is provided on the other side of the electrolyte membrane; a power control unit for applying a voltage Va between the reduction electrode and the oxygen evolving electrode; wherein the electrochemical reduction device is further characterized by a circulation pathway that connects the organic material storage tank and the reduction electrode of the electrode unit, the organic liquid passing through the circulation pathway; a concentration measurement unit for measuring a concentration of the aromatic compound to be supplied to the reduction electrode; and a raw material supply amount adjustment unit for adjusting the amount of the organic liquid including the aromatic compound to be supplied to the reduction electrode per unit time based on the concentration of the aromatic compound measured by the concentration measurement unit, wherein the raw material supply amount adjustment unit is configured to increase the amount of the organic liquid to be supplied to the reduction electrode when the concentration of the aromatic compound is decreased.