PURPOSE: To form an original image on a photosensitive body clearly without any distortion by adjusting the running courses of an exposure lamp and at least either of reflecting mirrors at right angles to their running courses and also at mutually orthogonal directions.

CONSTITUTION: The exposure lamp 1 and reflecting mirrors 2 and 3 are fixed to support bodies 46 and 47 and movable by a guide rod 48 and a guide rail 49 as shown by an arrow 50, and reflecting mirrors 9 and 10 are fixed to support bodies 51 and 52 and movable by a guide rod 53 and the guide rail 49 as shown by an arrow 50. The fitting hole 93 of a support member 91 which supports the guide rod 53 is formed thin and long in the right-left direction perpendicular to the moving direction of the reflecting mirrors 9 and 10, and the fitting hole 95 of the other support member 92 is extended thin and long in the up-down direction perpendicular to the moving direction. Therefore, the guide rod 53 is adjusted and fixed in parallel to an optical axis while confirming through a measuring jig, and a distortion-free original image is formed.