Abstract: Disclosed herein are an apparatus and method for reducing nitrate using iron-oxidizing microorganisms, which can easily reduce nitrate using iron-oxidizing microorganisms. The apparatus includes: a nitrate-reducing reactor which is operated under anaerobic conditions and provides a space for reduction of nitrate; and an iron-oxidizing microorganism provided in the nitrate-reducing reactor, wherein the iron-oxidizing microorganism releases divalent iron (Fe2+), the released Fe2+ is converted to Fe3+ by microbial oxidation under anaerobic conditions while releasing an electron, and the released electron is used in the reduction of nitrate into nitrogen gas by the iron-oxidizing microorganism.