| 摘要 |
PROBLEM TO BE SOLVED: To prevent a stop shape from deteriorating on a monitor sensor, even when a laser beam is made incident on a deflector by forming an angle in a sub-scanning direction. SOLUTION: A laser beam emitted from a semiconductor laser 10 is made incident on a polygon mirror 14 by forming the angle in the sub-scanning direction, reflected and deflected on the polygon mirror and reflected on a curved- surface mirror 15. Then, in reaches a photoreceptor drum 18 through an anamorphic lens 16 and an optical path deflection mirror 17. A separation mirror 40 separating luminous flux outside a scanning range is arranged on this side of the lens 16. Thus, reflected monitor light is condensed on the monitor sensor 42a through a cylindrical lens for monitor 41a. The lens 41a is arranged, so that a principal meridian M which is projected on a planar surface P which is almost vertical to the monitor light and which shows main power being inclined at an angle ofθ3 with respect to a direction (z), orthogonally crossed with a direction (y) in which the monitor light is used for scanning.
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