An object of the present invention is to provide, a cyclic carbonate and an aliphatic monohydric alcohol as starting materials, continuously feeding the starting materials into the continuous multi-stage distillation column A in which a catalyst is present, reactive distillation in said column A was carried out, low boiling point reaction mixture containing a dialkyl carbonate and the aliphatic monohydric alcohol to generate from the tower top (a _T) continuously withdrawn in a gaseous form, a high boiling point reaction mixture containing a produced diol from a lower portion of the column ( withdrawn a _B) continuously in a liquid form, the high boiling point reaction mixture (a _B) was continuously fed into the continuous multi-stage distillation column C, lower than the diol contained in the high boiling point reaction mixture (a _B) the boiling materials column bottom component obtained by distilling off the (C _B) was continuously fed into the continuous multi-stage distillation column C as column top component (C _T) and / or the side cut component (C _S), the continuous multi-stage distillation column C By acquiring diol as a side cut component from a side cut outlet (E _S), to provide a specific apparatus and process for producing the diol. And by the, for example, diol 1 ton or more per hour, preferably 2 tons or more, and more preferably in an amount of more than 3 tons, a long period (e.g., 1000 hours or more, preferably 3000 hours or more, more preferably over 5000 hours) to provide a concrete inexpensive industrial apparatus and industrial production process that can stably manufacture. According to the present invention, using a continuous multi-stage distillation column C having a specified structure, from the side cut outlet installed in the lower portion of the chimney tray having installed a specific structure at its enriching section, extracting a component of the liquid by the above problems can be achieved.