| 摘要 |
Plural linear marks extending along a scanning direction are spaced apart from each other at constant intervals and parallel to each other at a boundary of partial exposure ranges. When the marks are repeatedly formed by two light beams while a position of the mark formed by one of the two light beams is moved in the scanning direction, a density within a predetermined region corresponding to the boundary is changed so as to become lighter as the intervals between the marks are increased. When plural linear marks, which extend along the scanning direction and are spaced apart from each other at constant intervals and parallel to each other at a boundary portion of partial exposure ranges, are formed by two light beams while a position of the mark formed by one of the light beams is moved in a direction perpendicular to the scanning direction, a density within a predetermined region is changed so as to become lighter as an amount of offset is reduced. Accordingly, on the basis of a change in density within the predetermined region, it is possible to detect a case in which offset in beam irradiating positions in the scanning direction and the direction perpendicular to the scanning direction is zero. Offset of beam irradiating positions at the boundary can be controlled to be zero.
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