A scanning optical device including a plurality of light source devices 1a-1d, a light beam converting system 3 for converting the light focus state of the plurality of light beams emitted from light emitting members of the light source devices, a deflecting member 5 for scanningly deflecting the light beam from the light beam converting system, and imaging optical members 6a-6d for imaging the light beam from the deflecting member upon scan surfaces 8a-8d corresponding to the light beams, respectively, wherein the light beam converting system is comprised of a plurality of optical elements 3a-3d formed integrally and each converting the light focus state of associated one of the light beams from the light source devices, and wherein the light source devices are fixed to a holding member 12 while the positions with respect to the associated optical elements are adjusted.