| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming device which may be downsized by arranging a synchronism detecting sensor in a position which overlaps on an effective writing region in a sub-scanning direction and where the optical path of a writing beam having image data is not shielded. SOLUTION: This image forming device has a laser beam generating means 1, a polygon mirror 4, plural scanning lenses 5 and 6 and the synchronism detecting sensor 11 which detects the laser beam before arriving at the effective image region on a photoreceptor 7 and outputs the synchronizing signal for controlling a writing start position in a main scanning direction. The synchronism detecting sensor 11 is arranged in the position which overlaps on the effective writing region in the sub-scanning direction and where the optical path of the writing beam having the image data is not shielded.
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