We search for a cultivation method for reducing the amount of mycotoxin contamination in wheat which has been an important pending question for the quality in actual producing field of wheat and the health hazard risk for customers. The present invention discloses a method of reducing the contamination amount of mycotoxin in cereals characterized in that one or more compounds A selected from the group consisting of ammonium salts; primary to quaternary ammonium salts, alkali metal salts, alkaline earth metal salts and polyvalent metal salts of phosphorous acid and phosphite ester are given to the cereals.