A method for producing acetic acid, comprising: a carbonylation reaction step of reacting methanol with carbon monoxide in a reaction vessel in the presence of a catalyst system containing a metal catalyst and methyl iodide as well as acetic acid, methyl acetate, and water to produce acetic acid; an evaporation step of introducing and heating a reaction mixture obtained in the carbonylation reaction step in an evaporator to separate the reaction mixture into a vapor stream and a residual liquid stream; a residual liquid stream recycle step of recycling the residual liquid stream to the reaction vessel; a lower boiling point component removal step of separating the vapor stream with a first distillation column into a first overhead stream rich in methyl iodide and acetaldehyde and a first acetic acid stream rich in acetic acid and of condensing and separating the first overhead stream to obtain an aqueous phase and an organic phase; a first overhead stream recycle step of recycling at least a portion of the aqueous phase and/or the organic phase to the reaction vessel; and an acetaldehyde separation and removal step of separating and removing acetaldehyde in a process stream, wherein with heating of the evaporator, (i) an acetaldehyde concentration in the aqueous phase is controlled to not less than 2340 ppm by mass; and (ii) a methyl acetate concentration in the aqueous phase is controlled to less than 19.0% by mass; and (iii) a methyl acetate concentration in the organic phase is controlled to less than 38.0% by mass, and at least a portion of the aqueous phase is treated in the acetaldehyde separation and removal step to recycle a residual liquid after the acetaldehyde separation and removal to the reaction vessel and/or the acetaldehyde separation and removal step and/or other processes. a carbonylation reaction step of reacting methanol with carbon monoxide in a reaction vessel in the presence of a catalyst system containing a metal catalyst and methyl iodide as well as acetic acid, methyl acetate, and water to produce acetic acid; an evaporation step of introducing and heating a reaction mixture obtained in the carbonylation reaction step in an evaporator to separate the reaction mixture into a vapor stream and a residual liquid stream; a residual liquid stream recycle step of recycling the residual liquid stream to the reaction vessel; a lower boiling point component removal step of separating the vapor stream with a first distillation column into a first overhead stream rich in methyl iodide and acetaldehyde and a first acetic acid stream rich in acetic acid and of condensing and separating the first overhead stream to obtain an aqueous phase and an organic phase; a first overhead stream recycle step of recycling at least a portion of the aqueous phase and/or the organic phase to the reaction vessel; and an acetaldehyde separation and removal step of separating and removing acetaldehyde in a process stream, wherein with heating of the evaporator, (i) an acetaldehyde concentration in the aqueous phase is controlled to not less than 2340 ppm by mass; and (ii) a methyl acetate concentration in the aqueous phase is controlled to less than 19.0% by mass; and (iii) a methyl acetate concentration in the organic phase is controlled to less than 38.0% by mass, and (i) an acetaldehyde concentration in the aqueous phase is controlled to not less than 2340 ppm by mass; and (ii) a methyl acetate concentration in the aqueous phase is controlled to less than 19.0% by mass; and (iii) a methyl acetate concentration in the organic phase is controlled to less than 38.0% by mass, and at least a portion of the aqueous phase is treated in the acetaldehyde separation and removal step to recycle a residual liquid after the acetaldehyde separation and removal to the reaction vessel and/or the acetaldehyde separation and removal step and/or other processes. <EOS>