| 摘要 |
PROBLEM TO BE SOLVED: To prevent noise such as an air whistle when a rotary polygon mirror is rotated fast. SOLUTION: For a propagation path L1 for a direct propagated sound, i.e., an air peep which is generated at a corner part 1a of a rotary polygon mirror 1 and directly reaches a lid member 60, a propagation path (L1+2L) for a reflected propagated sound which is reflected by a bottom surface 50a of an optical box 50 and reaches the lid member 60 is constituted so that the length is 1/2λlonger; the two sound waves are made to interfere with each other, thereby reducing the vibration of the lid member 60 and the noise. |
