JPS6258484B

PURPOSE:To form an accurate edge although the edge of an irradiation pattern cross obliquely the deflected scanning direction, by turning an intermediate slit so that an image of the intermediate slit edge formed by an objective lens is in contact with the edge of the pattern to be formed. CONSTITUTION:A pair of slit plates 20a and 20b are formed into a semicircle having a chord of a linear edge. The circumference of the semicircle is supported by circular guides 23a and 23b and in a rotatable way centering on the center spots 21a and 21b of the edge. The scanning line (j) of the laser beam crosses a slit plate at the spots 21a and 21b. The width (b') with the scanning width limited by the plates 20a and 20b has no change although the plates 20a and 20b are turned centering on the intersections 21a and 21b by a motor 35 via gears 33 and 32. Accordingly the edge direction of the slit plate can be freely controlled.