A protruding locking pawl is provided at an end of a light guide which corresponds to a first light input surface. A recessed locking portion is formed in a frame so that the locking pawl can be locked in the locking portion. A light blocking member is slidably loosely inserted into a position where the light blocking member covers a longitudinal end of the light guide which corresponds to a second light input surface. Even if expansion and contraction occurs in the longitudinal direction of the light guide, the design dimensions of a first gap A and a second gap B can be maintained; the first gap A is formed between the first light input surface and a first light source, and the second gap B formed between the second light input surface and a second light source. Therefore, possible leakage current can be prevented.