PURPOSE: To fix an extension certainly and strongly without using an adhesive by equipping the extension with an elastic detent piece and a screw mounting part.

CONSTITUTION: An elastic detent piece 40 and a screw mounting part 41 are furnished on an extension enclosing a condenser lens. The elastic detent piece 40 is detained elastically with a detaining part 43 provided on the body 10 of lighting fixture, while the screw mounting part 41 is fastened to the fixation part of the lighting fixture body 10. This simplifies the mounting and removing works, provides more stable and strong fixation than when an adhesive is used, liberates from risk of exfoliation due to secular change of adhesive, ensures the long term stability, and enhances the working effectiveness.