A distillation apparatus includes a rectifying column, a stripping column located above seen from the rectifying column, a liquid sump unit located at a predetermined stage of the stripping column and configured to hold liquid that has flowed downward, a heat exchanger located in the liquid sump unit, a second pipe for introducing vapor in the rectifying column to the heat exchanger of the stripping column, and a third pipe for introducing fluids flowing out from the heat exchanger of the stripping column to the rectifying column. Further, a flare line having lower pressure than pressure in the rectifying column is connected to a downstream side of the third pipe. The distillation apparatus can switch a first flow toward an inside of the rectifying column through the third pipe to a second flow branching from the third pipe toward a pipe at a lower pressure side.