PURPOSE: To position a pre-correcting lens by a simple means by simplifying part replacing work.

CONSTITUTION: A lamp light source 20 where a mercury lamp 6 is housed in a lamp house 7 is arranged opposite on an inside surface of a face panel 5, and a main correcting lens 3 is interposed between the face panel 5 and the lamp light source 20, and projection light from the mercury lamp 6 is radiated to the inside surface of the face panel 5 through the main correcting lens 3, and the inside surface of the face panel 5 is exposed. The lamp light source 20 is formed on a opposed surface of the face panel of the lamp house 7, and has an opening recessed part 8 exposed by a light emitting part 9 of the mercury lamp 6 through a slit 11. A transparent plate 12 is fastened to this opening recessed part 8, and is sealed airtightly by a ring 13, and a pre-correcting lens 21 is placed on the transparent plate 12 through an XYθ position indexing mechanism 25 so as to be mountable and demountable freely, and the pre- correcting lens 21 is arranged in a position in the vicinity of the light emitting part of the mercury lamp 6 of the lamp light source 20 so that XYθ positions can be adjusted.