A method and apparatus for producing vinegar by acetic acid fermentation utilizing an automatic alcohol analyzer for measurement of alcohol concentration in a fermenting broth, a feeding apparatus for feeding alcohol solution as raw material to the fermenting broth, and a control computer controllably coupled to the alcohol analyzer and to the feeding apparatus. The alcohol concentration in the fermenting broth is periodically measured by the automatic alcohol analyzer by a direction from the control computer at given intervals over a plurality of cycles of measurement; the control computer calculates a feed rate of alcohol solution as raw material to the fermenting broth so as to control the alcohol concentration in the fermenting broth at a desirable concentration on the basis of a difference between a measured alcohol concentration in the fermenting broth and a desirable alcohol concentration and the alcohol consumption rate calculated during each of the cycles by the control computer; and then the feeding apparatus is operated to control the feed rate of the alcohol solution responsive to a control signal generated by the control computer as a result of the aforementioned calculations, to thereby controllably feed alcohol solution as raw material to the fermenting broth.