PURPOSE: To adjust a distorted picture and a local defocusing without individual adjustment of the optical system of 1st and 2nd carriages by linking the 1st and 2nd optical systems with a link member.

CONSTITUTION: Fixing screws 28, 35 of mirror bases 26, 33 of 1st and 2nd carriages 11, 12 are loosened respectively to move the mirror base 26 by a prescribed quantity and the distorted picture is corrected by adjusting the angle and fixed again by tightening the fixing screw 28. In this case, the mirror base 35 of the carriage 12 is moved in the same direction by a half the moving distance of the mirror base 26 by the movement of the mirror base 26 through a dynamic pulley 31 and a wire 36 to prevent occurrence of local defocus. Thus, the distorted picture is corrected and the occurrence of the local defocus at the correction is prevented by only the adjustment of the mirror base 26 in the carriage 11 and the workability is improved.