Patent ID: 7130096

Claim:
A light beam scanning apparatus comprising: a light source portion which emits a light beam; a rotary polygon mirror having a plurality of deflection surfaces, which deflects the light beam incident on the plurality of deflection surfaces by rotating on a rotation axis; and an imaging optical system which scans and images the light beam deflected by the rotary polygon mirror on a scanned surface to thereby form a latent image on the scanned surface, wherein a position which is a center of an effective scanning range of the light beam in a scanning direction and on which the latent image is formed on the scanned surface is set to be apart from an optical axis of the imaging optical system by a distance β along the scanning direction; and an angle α between a center of luminous flux of the light beam incident on the deflection surfaces of the rotary polygon mirror and an optical axis of the imaging optical system is set to satisfy a following relational expression to thereby form a ghost image on a region out of the effective scanning range (4π/ N )−( W/D )≦|α|<(4π/ N )−{( W−β )/ D} in which N is the number of deflection surfaces of the rotary polygon mirror, D is the optical length from an image-side principal point of the imaging optical system to the scanned surface, and W is a half width of the effective scanning range in the scanning direction.