PURPOSE: To make the width of a line constant and distinct and to change continuously the width of the line on occasion, by describing the line with an annular spot of a real image which is formed an image through a conical lens which is inserted in the optical path of an optical system for exposure.

CONSTITUTION: An optical table 20 is attached to an output terminal 19 of an optical fiber 18, and this output terminal 19 is used as a divergent spot light source, and the light from this light source is allowed to pass through a conical rotating lens 4A and a lens system 21 arranged on the optical table 20 to generate an annular spot 23 on a fixed photosensitive film 22. For the purpose of changing the diameter of the annular spot 23, the lens 4A is arranged so as to be movable in the direction of the optical axis on a moving mechanism 24. This optical system is arranged on the optical table 20, and the optical table 20 is installed on an XY moving mechanism 25 to expose linearly the surface of the photosensitive film 22 to light in accordance with the two-dimensional movement of the optical table 20 for the photosensitive film 22. The exposure distribution of a width 8 of this line is shown by a curve 9, and thus, the width of the line is made constant and distinct, and the width of the line is changed easily.