A light guide 11 of a rectangular cross-section has side faces 11a, 11b including short sides in the longitudinal direction of which one side face 11a is provided with a light-scattering pattern 20, formed by screen-printing in white paint, for scattering the light incident to the light guide 11. The other side face 11b facing the side face 11a is exposed from a casing 12 to serve as a light-emitting surface. In the present embodiment, it is possible to secure a sufficient amount of light because the whole area of the side face is used as the light-emitting surface. The remaining side faces 11c, 11d of the light guide 11 are side faces including the long sides. Since the side faces 11c, 11d easily produce a surface sink during molding, neither the light-scattering pattern 20 nor the light-emitting surface is provided thereon.