PURPOSE: To provide a safe substance capable of suppressing increase of blood pressure by effectively inhibiting an angiotensin converting enzyme and provide a food raw material containing the angiotensin converting enzyme inhibitor in concentrated state and widely usable as a food.

CONSTITUTION: A soybean protein solution is decomposed with a proteolytic enzyme and an insoluble matter is removed by centrifugation and filtration and the filtrate is directly poured into a column in which a reverse phase-based filler is packed to make an angiotensin converting enzyme inhibitor adsorbed and then, the inhibitor is eluted with a hydrated alcohol to concentrate the angiotensin converting enzyme inhibitor.