ROTARY POLYGON MIRROR DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a rotary polygon mirror device excellent in the deflection scanning performance of a light beam by preventing air accumulation from being caused at a window part with the rotation of a rotary polygon mirror, straightening an air current flowing along the rotary polygon mirror and restraining the up-and-down motion of the rotary polygon mirror. SOLUTION: An angleβformed by a notched surface 3a positioned on the front side of the window part in the rotating direction of the rotary polygon mirror with a line linking the outer end 3a0 of the notched surface and the center of rotation 0 of the rotary polygon mirror is regulated to a value satisfying 0.5×(180 deg.-360 deg./N)±10 deg. (provided that N is the number of the surfaces of the rotary polygon mirror).