It is intended to provide a process for safely and less expensively producing a fermented plant extract containing an immunopotentiator at a high concentration. Namely, a fermentation and culture method which comprises fermenting a plant material such as wheat flour by using Pantoea agglomerans which is a gram-negarive bacterium living in a symbiotic relation with a plant such as wheat or apple. Thus, the immunopotentiation action of the plant can be extremely enhanced. Moreover, such a product has a high safety because of being free from contamination with animal-origin impurities.
