PURPOSE: To easily concentrate cow's milk in high efficiency without decomposing useful components, by removing water from the milk using an inorganic porous membrane having a pore diameter of ≤10.

CONSTITUTION: Water in cow's milk is removed by pervaporation method using an inorganic porous membrane having pore diameter of ≤10 (e.g. porous α-Al2O3 membrane having pore diameter of ≤10) as a separation medium and keeping the milk-side pressure at about 1W1.5atm. and reverse-side pressure at about 50W10Torr. The substance attached to the separation medium, e.g. thin film on milk is scattered by intermittently blasting gas such as air against the separation medium.