A method for producing acetic acid while inhibiting by-production of acetaldehyde by increasing the carbon monoxide partial pressure or the methyl acetate content, comprising the steps of: continuously reacting methanol with carbon monoxide in the presence of a rhodium catalyst, an iodide salt, methyl iodide, methyl acetate, and water, said rhodium catalyst being a rhodium complex soluble in the reaction mixture under reaction conditions or a rhodium catalyst that can form such a rhodium complex; producing acetic acid at a production rate of 11 mol/L·hr or more; feeding and purging carbon monoxide to maintain a carbon monoxide partial pressure in the gaseous phase of a reactor of 1.05 MPa or more during the continuously reacting; recycling methyl acetate to maintain a methyl acetate content of the reaction mixture of 2 to 10 percent by weight during the continuously reacting; keeping the acetaldehyde content of the reaction mixture to 500 ppm or less; and keeping the production rate of acetaldehyde to 1/1500 or less of the production rate of acetic acid, wherein the reaction is carried out at a water content of the reaction mixture of 0.1 to 3 percent by weight and at a hydrogen partial pressure in the gaseous phase of the reactor of 70 kPa or less, the method further comprising a purification process which comprises the steps of: separating the reaction mixture into a volatile component and a low-volatile component by distillation, the volatile component comprising acetic acid, water, methyl acetate, and methyl iodide, and the low-volatile component comprising the rhodium catalyst and the iodide salt; separating the volatile component into a high-boiling component and a low-boiling component by distillation, the high-boiling component comprising acetic acid, and the low-boiling component comprising water, methyl acetate, and methyl iodide; recycling the low-volatile component to the reactor; separating and removing carbonyl impurities from the low-boiling component obtained in step to yield a residual component; and recycling the residual component obtained in step to the reactor. continuously reacting methanol with carbon monoxide in the presence of a rhodium catalyst, an iodide salt, methyl iodide, methyl acetate, and water, said rhodium catalyst being a rhodium complex soluble in the reaction mixture under reaction conditions or a rhodium catalyst that can form such a rhodium complex; producing acetic acid at a production rate of 11 mol/L·hr or more; feeding and purging carbon monoxide to maintain a carbon monoxide partial pressure in the gaseous phase of a reactor of 1.05 MPa or more during the continuously reacting; recycling methyl acetate to maintain a methyl acetate content of the reaction mixture of 2 to 10 percent by weight during the continuously reacting; keeping the acetaldehyde content of the reaction mixture to 500 ppm or less; and keeping the production rate of acetaldehyde to 1/1500 or less of the production rate of acetic acid, wherein the reaction is carried out at a water content of the reaction mixture of 0.1 to 3 percent by weight and at a hydrogen partial pressure in the gaseous phase of the reactor of 70 kPa or less, separating the reaction mixture into a volatile component and a low-volatile component by distillation, the volatile component comprising acetic acid, water, methyl acetate, and methyl iodide, and the low-volatile component comprising the rhodium catalyst and the iodide salt; separating the volatile component into a high-boiling component and a low-boiling component by distillation, the high-boiling component comprising acetic acid, and the low-boiling component comprising water, methyl acetate, and methyl iodide; recycling the low-volatile component to the reactor; separating and removing carbonyl impurities from the low-boiling component obtained in step to yield a residual component; and recycling the residual component obtained in step to the reactor.