To form an air flow entering from an upper opening and going out from a lower opening and thereby to exhaust foreign substances residing in an upper and lower lamp chambers to the outside of the lamp chambers by carrying them along with the air flow.

Because a gap S is formed between a tip of a partition 7 and an outer lens 5, the air blown in from an opening 10 of an upper lamp chamber 8 enters into a lower lamp chamber 9 from the upper chamber 8 through the gap S, and is exhausted from a lower opening 11. Thus, an air flow entering from the upper opening 10 and going out from the lower opening 11 is formed, so that foreign substances residing in the upper and lower lamp chambers 8, 9 can be exhausted outside the lamp chambers 8, 9 by carrying them along with the air flow.