PURPOSE: To provide a part mounting structure of high durability by restricting a motion other than the relative turn of a pivot and a bearing section.

CONSTITUTION: A contact section 20 on the internal side the first projection 2 of a movable reflector 13 is kept in contact with the external tapered surface or spherical surface 30 of the second projection 3 of a lamp housing 10, thereby restricting a motion other than the relative turn of a pivot 14 and a carrier 140 (i.e., vertical or right and left turn of reflector 13). According to this construction, the pivot 14 of the reflector 13 and the carrier 140 of the housing 10 give the same motion. Thus, the wall of the prepared hole 131 where the threaded section 141 of the pivot 14 of the reflector 13 is screwed, becomes free from a concern about a breakage, resulting in the improvement of durability.