| 摘要 |
PROBLEM TO BE SOLVED: To reduce the deviation of the length of a scanning line of a plurality of light beams. SOLUTION: An emitting optical system to emit the light beam, a polygon mirror 21 which deflects the light beam from the emitting optical system, and a scanning image-formation optical system which scans the light beam from the polygon mirror 21 to the surface to be scanned are provided. The scanning image-formation optical system has a scanning image-formation mirror 22 having the prescribed curvature in the main scanning direction and the sub-scanning direction, and in which the curvature of the main scanning direction changes when the position of the sub-scanning direction differs. The position of the sub-scanning direction in which each light beam of the emitting optical system is made incident on the scanning image-formation mirror 22 is set so as to reduce the deviation of the length of a scanning line which each light beam of the emitting optical system draws in the surface to be scanned.
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