| 摘要 |
PROBLEM TO BE SOLVED: To enhance optical performance by preventing luminous flux from being returned to a semiconductor laser beam source. SOLUTION: Since the luminous flux reflected from the surface 33b of a diaphragm 33 becomes a returned light beam C returned to the semiconductor laser beam source 21 by an identical locus to an emitted optical path when the angle of the surface 33b is 90 deg., such control that the light quantity of the beam source 21 becomes erroneous because it is erroneously detected is executed by a circuit substrate 28 controlling the light quantity of the beam source 21 in a scanning optical device. Therefore, when the surface 33b of the diaphragm 33 having a diaphragm hole 33a is provided with the angleθwith respect to the optical axis of the light source 21, the beam C reflected from the diaphragm 33 is prevented from being returned to the beam source 21.
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