PURPOSE: To easily excite a traveling wave for preventing the adhesion of toner and to effectively use an energy which is thrown in from an exciting source to an aperture electrode for exciting the traveling wave.

CONSTITUTION: An aperture electrode 1 consists of an insulating layer 106 shaped into an endless form; a modulation control part 13 composed of apertures 11 provided on a flat part of the insulating layer 106 on the side of conter electrodes, a control electrode layer 108, and a reference electrode layer 107; and a toner clouder part 14 provided on a flat part of the insulating layer 106 opposed to the modulation control part 13. An exciter 2 for exciting a traveling wave is provided on the aperture electrode 1. The exciter 2 consists of first and second piezoelectric bodies 21, 22 provided on the rear surface of the insulating layer 106. By applying an electric signal of a predetermined frequency to the first and second piezoelectric bodies 21, 22 at the time of image forming, the aperture electrode 1 is excited by a traveling wave in bending vibration.