A flat fluorescent lamp includes a lamp body and an external electrode. The lamp body includes a plurality of discharge spaces. Each of the discharge spaces includes a first discharge region having a first space width and a first space length, a second discharge region having a second space width and a second space length, and a third discharge region having a third space width and third space length. The second discharge region is disposed between the first and third discharge regions. The second space width is smaller than the first and third space widths, and the second space length is smaller than the first and third space lengths. Thus, an electrode part of the flat fluorescent lamp is prevented from being blackened due to dendrite generated at the electrode part, so that the display quality of the liquid crystal display device having the flat fluorescent lamp can be improved.