This study aimed to propose economic evaluation method for installing oil-water separation equipment into wastewater treatment system to attain energy recycling system in a food processing factory using Value Function （VF） and Separative Work Unit（ SWU） of separation engineering. VF for calculating SWU was determined by the field investigation at the food processing factory, Naoetsu-Yushi Co. Ltd. The results showed the required ability of the oil-water separation equipment to obtain a profit as at least 10% in this simulation for the food processing factory. More, the recovery period（ payback time） of the initial cost for installing the oil-water separation equipment and the wastewater treatment facility at 0% of discount rate was calculated as 162.6 months, which was shorter than the lifetime of them and it shows the economic feasibility of installing the oil-water separation equipment. The proposed method could achieve the comparison of different equipment or different conditions for total performance improvement, and help the selection of the alternative equipment or the implement of the surrounding condition.