The method of the present invention involves performing the deodorization step before the hydrogenation step and carrying out the hydrogen addition reaction under mild conditions effective to prevent the hardening of edible oil and trans fatty acid production, resulting in the production of processed edible oil having an enriched buttery flavor that is 100-fold stronger than the conventional hydrogenated oil with no unpleasant smell and a very low trans-fatty acid content. Further, the processed edible oil prepared according to the method of the present invention, even with the addition of only a small amount to conventional edible oil, food and feed products, is capable of providing an enriched buttery flavor without increasing the trans-fatty acid content or unpleasant smell and is, thus, useful as a substitute oil for hydrogenated vegetable oil.