PURPOSE: To enable parts to be easily replaced in an easily operating manner by a method wherein both ends of a jacket inner tube, a jacket outer tube, and a hot wire cut filter are pinched, in a detaching free manner, between an upper support material and a lower support material which are composed by dividing a cross section into two parts.

CONSTITUTION: A support material arranged symmetrically at both ends is composed of an upper support material 12 and a lower support material 13 by dividing a cross section into two parts. An end part of a jacket inner tube 16 is so constructed as to protrude further from an end part of a jacket outer tube 18. Further, both ends of a hot wire cut filter 19 are so constructed as to protrude from the end part of the jacket outer tube 18. A filter presser 22 provided to an inner surface of the lower support material 13 is so constructed as to absorb expansion by heat by establishing to have a 1 to 2mm space from the both ends of the hot wire cut filter 19. Therefore, by removing the upper support material 12, the jacket inner tube 16, the jacket outer tube 18, the hot wire cut filter 19, and a high pressure metal vapor discharge lamp 20 are taken out, and the hot wire cut filter 19 and other parts which are likely to impair can be exchanged.