Cold cathode fluorescent tubes of the first group are aligned widthwise in one side of an enclosure which is divided into two areas at a centerline running widthwise. Cold cathode fluorescent tubes of the second group are aligned widthwise in the other side of the enclosure. All of the cold cathode fluorescent tubes are symmetrically-placed with respect to the centerline running widthwise. The cold cathode fluorescent tubes positioned outside widthwise are inclined at θ2 so that the distance between each of the tubes and the aperture plane gradually decreases lengthwise from an edge toward the center of the enclosure. The cold cathode fluorescent tubes positioned inside widthwise are inclined at θ1 so that the distance between each of the tubes and the aperture plane gradually decreases lengthwise from an edge toward the center of the enclosure. The inclined angle θ1 is made greater than the inclined angle θ2.