A long decorative illumination device according to one or more embodiments may include a plurality of light guide plates configured to reflect light entering therein from an end surface thereof with reflection surfaces formed in recesses thereon, and causing the light to be emitted from a light emitting surface thereof; a plurality of light sources provided corresponding to the plurality of light guide plates; and a long window part open from at least two directions of the front surface and side surfaces of the decorative illumination device; and the plurality of light guide plates is slanted with gaps therebetween, so that in the slanted state the light emitting surfaces thereof are oriented toward the window part.