[Problem] To stably hold an electric potential effect to be imparted to an object, by making the effect of an electric charge on an object to be sufficient to more reliably demonstrate the preservation efficacy of an electric charge, and controlling the flow of electric current in a loaded portion of the object. [Solution] The present invention is provided with: an electroconductive enclosure structure disposed above and/or both above and below a mounting part (1) and used for enclosing the area above and/or both the areas above and below as viewed from an object (O) mounted on a mounting surface； a first electrode (21) in contact with an upper part position near one side part (11S) of the mounting part (1)； a second electrode (22) in contact with a lower part position near the other side part (12S) of the mounting part (1)； a third electrode (23) in contact with a position near one side part of the enclosure structure； a fourth electrode (24) in contact with a position near the other side part of the enclosure structure； and voltage supply units (20) electrically connected to the electrodes, respectively. The voltage supply units (20) simultaneously apply a negative DC voltage and an AC voltage to one and the other of the first electrode (21) and the second electrode (22), respectively.
