To provide a colored lights mixing device emitting uniform light with rich color variations.
Different colored light is emitted from at least one light source set 1 comprised of three color light source units. A light mixing plate 2 made of a transparent plate has a bottom undulating surface 21 and a top undulating surface 22 with lines in different directions from each other. When each light source unit is lighted, the projected single color light passes the bottom undulating surface 21 and is mixed inside the light mixing board 2 to form linear rays. When the linear rays pass the top undulating surface 22, the rays become a synthesized color light distributed uniformly above the light mixing board 2.