A vehicular headlamp includes a lamp body having an opening, a first reflector disposed within the lamp body, a lens, and a second reflector. The second reflector serves as an extension reflector to cover a gap between the opening of the lamp body and the first reflector. The lens and the second reflector are joined together at an edge portion thereof by laser welding. The second reflector has a leg portion on a back surface thereof. An edge portion of the opening has a groove to receive the leg portion, and seal material having a predetermined adhesibility, which can be pulled off, is injected into the groove. The second reflector joined to the lens is mounted on an edge of the opening of the lamp body via the seal material.