PURPOSE: To efficiently separate and concentrate on object substance such as butanol by an osmotic vaporization method by using an impregnation-type liq. membrane obtained by appropriately combining a porous carrier and an extractant.

CONSTITUTION: The extractant is selected from materials having a high distribution coefficient to the object substance to be separated and concentrated in a soln., a low distribution coefficient to the solvent dissolving the object substance, and a higher b.p. than the object substance, and which is not vaporized in the vapor phase side (under reduced pressure). For example, when butanol is separated from an aq. butanol soln. and concentrated, oleyl alcohol is used as the extractant, an impregnation-type liq. membrane formed by impregnating a carrier of a porous polypropylene membrane, etc., with oleyl alcohol is used, and an object substance such as butanol is separated and concentrated by an osmotic vaporization method.