A charging device includes a rotatable screw gear, a motor, a support, and a protruding member. The screw gear is positioned along length of a linear electrode. The motor rotates the screw gear in forward and reverse directions. The support holds the cleaning member mounted so as to be in contact with the electrode, and is mounted unrotatably but reciprocably between a first end and a second end of the electrode. The member extends perpendicular to the length of the electrode from the support, and has a projection for being elastically fitted into a thread groove of the screw gear along a radial direction of the screw gear. The member is configured in such a manner that a distance between a starting point of elastic deformation of the member and a contact point between the projection and a thread of the screw gear differs according to whether the support is moved forward or backward.