Disclosed is a lactic acid production method by separating lactic acid produced in a culture solution by means of the fermentation culture of a microorganism. Specifically disclosed is a lactic acid production method, which comprises: a step (A) of filtering the culture solution through a nano-filtration membrane; and a step (B) of distilling a lactic-acid-containing solution produced in the step (A) under a pressure ranging from 1 Pa to the atmospheric pressure (inclusive) at a temperature ranging from 25 to 200° C. (inclusive) to collect lactic acid. The method can effectively remove an inorganic salt dissolved in a fermentation culture solution or contained in the fermentation culture solution in the form of a poorly soluble solid material by a simple manipulation, enables to prevent the racemization or oligomerization of lactic acid during the process of producing lactic acid, and therefore can produce lactic acid in a high yield.