PROBLEM TO BE SOLVED: To provide a processed food of citrus fruits utilizing all active substances of fruits including epicarps and seeds of citrus fruits, suppressing intensity of sourness to eat easily, processing only fruits containing the epicarps and seeds without additives, and making it easy to utilize them as health food or health functional food.SOLUTION: Only citrus fruits containing epicarps and seeds are filled in a container. The container filled with the fruits is put in a storeroom. The fruits are blacken by warming them in a temperature range of 55-85°C and maturing them for a period of 70-90 days.