A flat panel display device includes a backlight system and a display panel, wherein: the backlight system includes a light source, a light homogenization mechanism, and a back frame; the back frame carries the light source and the light homogenization mechanism and the back frame includes at least first and second primary assembling pieces, wherein the first primary assembling piece has an end forming at least two joint sections, each of the joint sections having a structure mating an end of the second primary assembling piece, the first primary assembling piece using one of the joint sections to join the corresponding end of the second primary assembling piece, the primary assembling pieces comprising positioning sections, the positioning section cooperating with a back panel of the flat panel display device to position the back frame. A stereoscopic display device and a plasma display device are also provided.