A preservation treatment apparatus for treating an object containing oxide into a preservable state comprising: a placing portion having a conductive placing surface on which the object is placed or an engaging portion having a conductive engaging surface with which the object is engaged; a conductive enclosure structure configured to be formed continuously with an upper portion of the placing portion or configured to be arranged in the vicinity of the placing portion in a spaced-apart manner, and surrounding at least one of both sides, front and rear sides and upper and lower sides of the object as viewed from the object placed on the placing surface; one or more sets of electrodes, each set of electrodes being constituted of a DC electrode which is brought into contact with either one of the placing portion and the enclosure structure and an AC electrode which is brought into contact with the other one of the placing portion and the enclosure structure respectively; a voltage supply portion electrically connected with respective electrodes which constitute the set of electrodes, the voltage supply portion being configured to supply a negative DC voltage to one electrode of each set of electrodes and to supply an AC voltage to the other electrode, wherein one electrode and the other electrode which constitute the set of electrodes are respectively arranged at symmetrical positions in a spaced-apart manner along extensions of a diagonal line direction on one plane expanding outwardly as viewed from the object placed on the placing portion or engaged with the engaging portion, in a state where at least any one of both sides, front and rear sides and upper side of the object as viewed from the object are surrounded by the conductor, the voltage supply portion simultaneously applies a negative DC voltage and an AC voltage to one and the other of the electrodes which are arranged in a spaced-apart manner along both directions along a diagonal line direction where the object is arranged close to the center on one plane expanding outwardly of either one of the placing portion and the enclosure structure which surround the periphery of the object respectively. a placing portion having a conductive placing surface on which the object is placed or an engaging portion having a conductive engaging surface with which the object is engaged; a conductive enclosure structure configured to be formed continuously with an upper portion of the placing portion or configured to be arranged in the vicinity of the placing portion in a spaced-apart manner, and surrounding at least one of both sides, front and rear sides and upper and lower sides of the object as viewed from the object placed on the placing surface; one or more sets of electrodes, each set of electrodes being constituted of a DC electrode which is brought into contact with either one of the placing portion and the enclosure structure and an AC electrode which is brought into contact with the other one of the placing portion and the enclosure structure respectively; a voltage supply portion electrically connected with respective electrodes which constitute the set of electrodes, the voltage supply portion being configured to supply a negative DC voltage to one electrode of each set of electrodes and to supply an AC voltage to the other electrode, wherein one electrode and the other electrode which constitute the set of electrodes are respectively arranged at symmetrical positions in a spaced-apart manner along extensions of a diagonal line direction on one plane expanding outwardly as viewed from the object placed on the placing portion or engaged with the engaging portion, in a state where at least any one of both sides, front and rear sides and upper side of the object as viewed from the object are surrounded by the conductor, the voltage supply portion simultaneously applies a negative DC voltage and an AC voltage to one and the other of the electrodes which are arranged in a spaced-apart manner along both directions along a diagonal line direction where the object is arranged close to the center on one plane expanding outwardly of either one of the placing portion and the enclosure structure which surround the periphery of the object respectively.