| 摘要 |
PROBLEM TO BE SOLVED: To enable designing which evades a decrease in optical performance by preventing luminous flux which is reflected by the reflecting surface of a deflecting means to a light source side from being imaged on a scanned surface. SOLUTION: The horizontal-scanning directional tilt angleθof the optical axis of a light beam which is made incident on a rotary polygon mirror 22A whose optical axis is slanted so that the position of the optical axis of the light beam which is reflected by a reflecting surface adjacent to the main reflecting surface of the rotary polygon mirror 22A and returns to the side of an LD 26 deviates from the center of the opening of an aperture 30 along a direction corresponding to the vertical scanning direction at the arrangement position of the aperture 30 by (W+S)÷2 (where S is the diameter of the light beam at the arrangement position of the aperture 30 and W is the size of the opening of the aperture along the direction corresponding to the vertical scanning direction) is so determined thatθ>=tan<-1> ((W+S)÷4L) (where L is the distance between the aperture 30 and the rotary polygon mirror 22A) and the LD 26 is slanted according to this tilt angleθ.
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