The present invention provides a backlight device, which comprises a plurality of optical devices and a plurality of backlight plates. The plurality of backlight plates include light sources, respectively, and are disposed at the light inlets of the plurality of optical devices. Then the beams of the light sources can be incident to the plurality of optical devices through the light inlets and reflected to the light outlets of the plurality of optical devices to form a backlight source for a display panel. The plurality of optical devices extend from the light outlets beyond the opposite surface of the display panel. By distributing optical paths, the spaces required for the optical paths can be reduced.