A light guide has first and second light guide parts (S, T) in front and rear of a constricted part (2). The first light guide has first and second side parts (1a, 1b). The second light guide part has a reflection condensing part (4) and third and fourth side parts extending from the constricted part to divert the first and second side parts more outward than imaginary surfaces (1c, 1d) as extensions of the first and second side parts beyond the constricted part.