This disclosure is directed to an illumination flat cable device having a light-transmissive frame of a flat shape, a reflective cover, an illumination strip and a flat cable. The light-transmissive frame has an illumination side, an illumination channel at the illumination side, a cabling side, and cable channels on the cabling side. Each cable channel is disposed in parallel with the longitudinal direction of the light-transmissive frame. The reflective cover on the illumination side has a reflective surface covering the illumination channel. The illumination strip in the illumination channel has a projecting direction disposed toward the reflective surface. The flat cable has conductive wires respectively disposed in the cable channels and a pair of connectors. The light-transmissive frame has a pair of end portions disposed corresponding to the pair of connectors.