To provide a practically excellent technique by which a large amount of γ-aminobutyric acid can safely, inexpensively and readily be produced in high concentration for the application of the activities for suppressing blood pressure elevation of the γ-aminobutyric acid to wide food.

Glutamic acid in an added solution and the glutamic acid in rice bran containing embryo or rice with the embryo are converted to the γ-aminobutyric acid by the enzymic action of a decarboxylase of the glutamic acid in the rice embryo, the rice bran containing the embryo or the rice with the embryo by adding a natural condensed soup containing the glutamic acid in high concentration or the aqueous solution of the glutamic acid to at least one kind of the rice embryo, the rice bran containing the embryo or the rice with the embryo, and reacting the resultant mixture by a high-efficiency whole body rotation type reactor.

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