A lamp unit is constructed of light sources, a reflector, a lamp housing that receives the light sources and the reflector therein, and a lamp lens that closes an opening of the lamp housing. The reflector has a through hole that is formed in a portion positioned above a first light source as a heat source, so that air warmed by heat of the first light source can be introduced into a rear side of the reflector via the through hole. The air introduced into the rear side of the reflector via the through hole and ascending therein can be lead by a first guide means to an air stagnating portion positioned in an end periphery of a hermetically-closed space that is defined by the lamp housing and the lamp lens.