PURPOSE: To draw patterns over a wide range and to reduce the time and labor for film formation considerably, by moving parallely and rotating the rectangular light spot formed with a single slit of variable sizes in accordance with plotting command.

CONSTITUTION: Light shielding plates 11, 11' for top and bottom, and light shielding plates 12, 12' for right and left are disposed in a photohead, and a slit aperture 13 is formed by control programs. The light spot 10 of a rectangular shape formed by the aperture is rotated by 180° in the end part P1 of a pattern 8, moves parallelly to P1→P2 and is rotated again by 180° at the P2, whereby the pattern 8 is drawn. All the movements and rotations for such drawing are accomplished in accordance with the instructions of the prescribed plotting commands, whereby prescribed exposure treatments are applied on the film. An extremely wide range of land patterns are thus drawn, and the time and labor for formation of films for producing printed wiring boards are reduced considerably.