Patent ID: 7098937

Claim:
A multi-beam scanning optical system, comprising: a light source having at least three light-emitting points; deflection means for deflecting at least three light fluxes emitted from the at least three light-emitting points to a surface to be scanned; and scanning optical means for guiding the at least three light fluxes which are deflected and reflected on the deflection means onto the surface to be scanned, each of the at least three light fluxes being entered into the surface to be scanned at an angle within a sub-scanning section, wherein, provided that a variation in lengths of scanning lines which is caused when each of the at least three light fluxes is entered into the surface to be scanned at an angle within the sub-scanning section is represented as ΔY 1 , a variation in lengths of scanning lines which is caused when each of the at least three light fluxes is allowed to enter as a non-parallel light flux to a deflection surface of the deflection means within a main-scanning section is represented as ΔY 2 , and a variation in lengths of scanning lines which is caused from a difference of wavelength between at least two of the at least three light fluxes is represented as ΔY 3 , values of ΔY 1 , ΔY 2 , and ΔY 3 are set so as to satisfy |Δ Y 1 +Δ Y 2 +Δ Y 3 |<|Δ Y 1 |.