| 摘要 |
PURPOSE:To prevent adverse influence on an image due to a synchronizing signal generating optical beam, by making scan an area except the latent image forming area of a photosensitive body, accompanied by the rotation of a rotary polygon mirror. CONSTITUTION:The laser beam printer is constituted so that a synchronizing signal generating laser beam B' is made incident on the reflecting plane 3a of a polygon mirror 3 diagonally from the upper side against a flat plane on which an image forming laser beam B is scanned, and after that, it is reflected diagonally to the lower side, and is made advance toward a synchronization control light receiving part 8. In other words, it is constituted so that, even when the synchronizing signal generating laser beam B' is scanned accompanied by the rotation of the polygon mirror 3, the synchronizing signal generating laser beam B' is prevented from arriving at the latent image forming area S of a photosensitive drum 4. In this way, no latent image which becomes the noise for a bit of picture information, is formed on the photosensitive drum 4, and deterioration in the image can be evaded.
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