PURPOSE: To perform an extractive distillation efficiently by supplying a gaseous hydrocarbon mixture contg. more proportion of component which is easily soluble in a polar solvent to the middle or lower part of an extractive distillation tower and a liquid hydrocarbon mixture contg. less proportion of a component which is easily soluble in the solvent to the upper part to the tower.

CONSTITUTION: In the case of using two kinds of paraffinic, olefinic or diolefinic hydrocarbons, a mixture contg. more proportion of the olefinic or diolefinic hydrocarbons which is easily soluble in a polar solvent is gasified in a vaporizer D through a pipe 1 and is fed into the middle stage F1 of the extractive distillation tower A. On the other hand, another mixture contg. less proportion of said easily soluble hydrocarbon is fed in the form of liquid to an upper stage F2 than the stage F1. A polar solvent (e.g.; DMF) are supplied 8 from around the tower top and extractive distillation is effected. From the tower top, ≥1 kinds of the paraffinic and/or olefinic hydrocarbon which is (are) hardly soluble in the solvent are discharged in the form of gas and is (are) removed through a pipe 3 after condensation and liquefaction C. From the tower bottom, ≥1 inds of the olefinic and/or diolefinic hydrocarbon is (are) discharged 5 together with the polar solvents and separated to the hydrocarbon and the polar solvent by feeding to a feeding stage of a diffusing tower B which is several stages lower than the top of the tower B.