Patent ID: 6882404

Claim:
A scanning optical device comprising: a plurality of light sources emitting a plurality of laser beams; an optical deflector for deflecting the plurality of laser beams with at least one deflection surface thereof; an incident optical system for introducing the plurality of laser beams to said optical deflector; and a scanning optical system for focusing the plurality of deflected laser beams onto a target surface to be scanned, wherein the width of the plurality of laser beams being larger than the width of the deflection surface in a main scanning direction, wherein principal rays of the plurality of laser beams, separated by a predetermined angle, cross each other near the deflection surface in a main scanning cross-section, and wherein said scanning optical device satisfies the following expression: Δθ<(4 π/N )×(1−ρ), where Δθ represents the largest angle between principal rays of two of the plurality of laser beams, N represents the number of deflection surfaces of said optical deflector, and ρ represents the scanning efficiency of the deflection surface, which is the ratio of an image forming range to the theoretical maximum scanning width by one deflection surface of said optical deflector.