PURPOSE: To constitute a distillation apparatus separating two substances approximate in saturated steam pressure without requiring a high distillation tower by dividing a distillation tower into a plurality of stages over the range from a raw material supply part to a product taking-out part to arrange the respective distillation towers in parallel in a horizontal direction and connecting the bottom parts of the distillation towers on a raw material supply side to the top parts of the distillation towers on a product taking-out side by liquid phase sully pipes and gaseous phase supply pipes.

CONSTITUTION: Distillation towers 1a-1c are constituted in a divided form over the range from a raw material supply part 2 to a product taking-out part 3 and arranged in parallel in a horizontal direction. The bottom parts of the distillation towers 1a, 1b on the side of the raw material supply part 2 and the top parts of the distillation towers 1b, 1c on the side of the product taking-out part 3 are allowed to communicate with each other by the liquid phase supply pipes 4ab, 4bc directed from the bottom parts to the top parts and the gaseous phase supply pipes 5ba, 5cb directed from the top parts to the bottom parts. Further, heating means are provided to the bottom parts of the distillation towers and cooling means are provided to the top parts of the distillation towers and pressure raising means are provided to the gaseous phase supply parts and flow rate control means are provided to the liquid phase supply pipes. As a result, an apparatus for separating two substances approximate in saturated steam pressure is constituted without requiring an extremely high distillation tower.