The present invention relates to a method for producing a carbonate compound and methacrylic acid or an ester thereof, containing a step (a1) of obtaining hexachloroacetone and hydrogen chloride from acetone and chlorine molecule, a step (a2) of obtaining a dialkyl carbonate and chloroform from hexachloroacetone and an alkyl alcohol, a step (b1) of obtaining 1,1,1-trichloro-2-methyl-2-propanol from chloroform and acetone, a step (b2+b3 or b4) of obtaining methacrylic acid or an ester thereof and hydrogen chloride from 1,1,1-trichloro-2-methyl-2-propanol and water or an alcohol, and a step (c1 or c2) of obtaining chlorine molecule by reacting hydrogen chloride with oxygen molecule.