A dust-screening member includes a plate-like light transmitting portion having a polygonal shape, and at least one plate-like side wall portion which tilts as much as a predetermined angle and extends from at least one side of the light transmitting portion so that they do not come in contact with each other. A vibrating member is fixed to one plate-like side wall portion and apples a vertical vibrational amplitude to the surface of the light transmitting portion. The light transmitting portion and the at least one side wall portion are formed to have a substantially uniform thickness by use of the same material. The light transmitting portion is positioned in front of an image forming element held by a holding member. The one side wall portion is fixed to the holding member at a position other than a position to which the vibrating member is fixed.