PURPOSE: To prevent discharge between two supports by fixing a covering body insulating between two supports, which are held by a base body while holding a discharge lamp, to the base body.

CONSTITUTION: The subject mounting construction is provided with two supports 19 and 20 to be connected to the external power supply, a base body 9 holding these supports 19 and 20, a discharge lamp 2 being held between two supports while being made to be conductive to the external power supply, and a cover body 21 being fixed to the base body 9 while insulating between two supports 19 and 20. Accordingly, a cover body 21 to be fixed to the base 9 insulates between two supports 19 and 20 salient from the cover body 21. Thereby, discharge between two supports can be surely prevented.