The present invention not only forms an electric field environment that can be controlled to differentiate between preservation of food freshness and promotion of ripening but also promotes fermentation by fermentative microbes, propagates plankton and inhibits bacterial reproduction. An electrode plate 2 is set inside a refrigerator 1 or an adjustable temperature box 6. Food 3 or a yogurt container 9 is place thereon. The electrode plate 2, 10 is connected to a power source 4, 11. Selection between food freshness preservation and promotion of ripening, and promotion of fermentation of fermented foods such as yogurt are performed by rectification, and voltage and frequency control of the power source. Additionally, propagation of phytoplankton and inhibition of bacterial reproduction are performed by controlling the frequency, voltage and ON/OFF timing of the power source.
