To simply carry out antiseptic treatment of wheat flour without impairing taste of wheat flour food itself.

Wheat flour 26 is put on an insulating table 25 which is used as a site of harmonic potential by a transformer 1 and subjected to harmonic voltage applying treatment to impart antiseptic property to wheat flour 26. The wheat flour 26 to which antiseptic property is imparted and water to which harmonic voltage is applied are used to produce wheat flour food or wheat flour food is washed with water to which harmonic voltage is applied to impart antiseptic property to wheat flour food.