A method for producing acetic acid in acetic acid production equipment, the equipment comprising: a reactor; a first distillation column; a second distillation column; and an additional purification unit, the method comprising: a reaction step of subjecting a material mixture comprising methanol, carbon monoxide, a catalyst, and an iodide to a methanol carbonylation reaction in the reactor to form acetic acid in a reaction mixture; a flash evaporation step of partially evaporating the reaction mixture to separate the reaction mixture into vapors and residual liquid components, wherein a portion of the vapors is introduced into the first distillation column as a crude acetic acid stream. a first purification step of subjecting a crude acetic acid stream to distillation in the first distillation column to give a first acetic acid stream, the crude acetic acid stream containing the acetic acid formed in the reaction step, the first acetic acid stream being enriched with acetic acid as compared with the crude acetic acid stream; a second purification step of subjecting the first acetic acid stream to distillation in the second distillation column as a dehydration column to give a second acetic acid stream enriched with acetic acid as compared with the first acetic acid stream; and a third purification step of subjecting an acetic acid stream to purification in the additional purification unit while controlling a corrosive iodine concentration in the acetic acid stream having a water concentration of 0.001 to 2 mass percent and passing through the additional purification unit to 100 ppm or less, to give a third acetic acid stream enriched with acetic acid as compared with the second acetic acid stream. a reactor; a first distillation column; a second distillation column; and an additional purification unit, a reaction step of subjecting a material mixture comprising methanol, carbon monoxide, a catalyst, and an iodide to a methanol carbonylation reaction in the reactor to form acetic acid in a reaction mixture; a flash evaporation step of partially evaporating the reaction mixture to separate the reaction mixture into vapors and residual liquid components, wherein a portion of the vapors is introduced into the first distillation column as a crude acetic acid stream. a first purification step of subjecting a crude acetic acid stream to distillation in the first distillation column to give a first acetic acid stream, the crude acetic acid stream containing the acetic acid formed in the reaction step, the first acetic acid stream being enriched with acetic acid as compared with the crude acetic acid stream; a second purification step of subjecting the first acetic acid stream to distillation in the second distillation column as a dehydration column to give a second acetic acid stream enriched with acetic acid as compared with the first acetic acid stream; and a third purification step of subjecting an acetic acid stream to purification in the additional purification unit while controlling a corrosive iodine concentration in the acetic acid stream having a water concentration of 0.001 to 2 mass percent and passing through the additional purification unit to 100 ppm or less, to give a third acetic acid stream enriched with acetic acid as compared with the second acetic acid stream. <EOS>