| 摘要 |
PROBLEM TO BE SOLVED: To obtain a scanning optical system capable of preventing dust from adhering to an optical system. SOLUTION: In the case of performing scanning exposure, a solenoid 340 is energized after the blast of pressurized air is started through a filter 306 by a fan 308 inward a partition 312, so that a shutter 304 becomes in an open condition shown by a solid line; therefore, the dust is prevented from entering inside the partition 312 through an aperture part 314, and the dust is prevented from adhering to a polygonal mirror 218, an fθlens 220, a cylindrical lens 221, a planar mirror 222, a reflection mirror 223 disposed inside the partition 312.
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