To prevent generation of gas containing material turning to a cause of blur and prevent blur of an optical system, by using seal material subjected to degasification treatment in a tightly closing structure part.

Seal material of a tightly closing structure part 52 tightly closing a mercury lamp 41, an oval mirror 42, a mirror 43 for bending, a collimator lens 44 and a bandpass filter 45 is subjected to degasification treatment. That is, concerning the seal material used for the tightly closing structure part 52, material turning to a cause of blur is regulated to be equal to or lower than a constant value. In addition, it is possible that resin material used for a cable, a piping tube, etc., grease using for lubricant of a driving part and adhesive agent used for fixing components or the like are subjected to degasification treatment. As a result blur of optical components (the mercury lamp 41, the oval mirror 42, the mirror 43 for bending, the collimator lens 44 and the bandpass filter 45) arranged in the tightly closing structure part 52 can be prevented.