PURPOSE: To prevent a splash of a mist generating just after gas-liq. mixed fluid is allowed to flow into a distillation column main body to a periphery of a baffle.

CONSTITUTION: The periphery of a starting material supply port 15 opening in the distillation column main body 1 so that a heated gas-liq. mixed fluid 7 is introduced is surrounded with a lower part opening baffle 17, and a slit 21 having very small width is formed at a part of the baffle 17. The mist 4b generating at the time of separating the gas-liq. mixed fluid 7 into gas and liq. in the baffle 17 reaches the slit 21 accompanied by a steam 4a in the baffle 17, most part of the accompanied mist 4b sticks to an edge part of the slit 21 having very small width and is removed from a flow of the steam 4a, and the mist becomes droplet by the mist 4b sticking one after another and runs down, the splash of the mist 4b to the periphery of the baffle 17 is prevented.