Provided is a process for producing acetic acid by carrying out reaction of methyl formate in the presence of a Group VIII metal catalyst, at least one iodine compound, acetic acid and carbon monoxide, continuously drawing a reaction mixture from a reactor, introducing the reaction mixture into a flash distillation zone, separating an evaporated component and an unevaporated component, recycling the unevaporated component to the reaction zone, and obtaining acetic acid from the evaporated component, wherein formic acid and methyl formate are allowed to coexist in the flash distillation zone and/or the recycling zone. According to this process, no loss of methyl formate and formic acid is caused and only methyl formate is used as a starting material with basically requiring no supply of carbon monoxide.