A pixel is formed by sealing an insulating liquid and floating particles in an area defined by a first substrate, a second substrate and partitions. The width of the partition has to be reduced in order to improve the pixel brightness by enlarging a flat electrode. In this case, the height of the partition has to be reduced for retaining the mechanical strength. If the height of the partition is reduced, an area of the partition electrode becomes small, thus failing to retain the memory effect. The planar surface of the partition is then formed into a zigzag shape so as to increase the area of the partition electrode.