To uniform the light distribution in a light guide.

In this light guide LG, the quantity of light emitted from the center part of an emitting end surface is made relatively little as compared with the quantity of light emitted from the peripheral part of the emitting end surface. For example, a mask 42 for cutting off light is provided in the vicinity of the emitting end of the light guide LG. For example, the mask 42 is circular and arranged centering around an optical axis Z0. By providing the mask 42, the emitted light from the center part of the emitting end surface is cut off centering around the optical axis Z0.