NOVELTY - An antioxidant is a mixture containing an amine compound chosen from p-phenylenediamine-type compound (I), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (II) and polymer of 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (II) having degree of polymerization of 2-5, a diphenylamine-type compound (III) and a phenothiazine (IV), and a phenol-type compound such as hydroquinone-type compound (V) and its derivative, tetrakis (methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)methane, isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, styrenated phenol and its polymer.    USE - Antioxidant is used for stabilized biodiesel fuel (claimed).    ADVANTAGE - The biodiesel fuel formed using the antioxidant has excellent oxidation-resistant stability and heat-resistant stability, with reduced usage of antioxidant, and suppresses generation of carbon in the engine. The generation of rubber-like substance obtained by oxidation polymerization of the fuel in engine or fuel tank, and deterioration of motor vehicle component such as fuel hose are prevented. The amount of nitrogen oxide derived from the antioxidant in the waste gas is reduced.    DETAILED DESCRIPTION - An antioxidant is a mixture containing an amine compound chosen from p-phenylenediamine-type compound of formula (I), 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline of formula (II) and polymer of 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (II) having degree of polymerization of 2-5, a diphenylamine-type compound of formula (III) and a phenothiazine of formula (IV), and a phenol-type compound such as hydroquinone-type compound of formula (V) and its derivative, tetrakis (methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate)methane, isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, styrenated phenol and its polymer.    R1=phenyl or 1-8C alkyl;    R2=3-10C alkyl;    R3,R4=H, 4-9C alkyl or aryl;    R5,R6=H or 1-8C alkyl;and    R7-R10=H or 1-4C alkyl.    An INDEPENDENT CLAIM is included for stabilized biodiesel fuel, which contains antioxidant (0.005-5 mass%) with respect to biodiesel fuel.