The present invention provides a flat panel display device of a flat panel display device, which comprise backlight system and a display panel. The backlight system includes a light source, a first primary assembling piece, a second primary assembling piece, a third primary assembling piece, a fourth primary assembling piece, a fifth primary assembling piece, a sixth primary assembling piece, and at least one secondary assembling piece. The first primary assembling piece, the second primary assembling piece, the third primary assembling piece, and the fourth primary assembling piece are joined to form a main frame structure of the back frame of the backlight system. The secondary assembling piece is arranged inside the main frame structure and joined to the main frame structure. The light source is arranged on the second primary assembling piece and the fourth primary assembling piece. The fifth primary assembling piece, the first primary assembling piece, the sixth primary assembling piece, and the third primary assembling piece are joined to form a central frame of the backlight system. The present invention also provides a stereoscopic display device. The flat panel display device and the stereoscopic display device of the present invention have a simple backlight structure, save the material for back frame, and thus lower down the cost of flat panel display device.