Multi-beam optical scanning device and image forming apparatus using the same

A multi-beam optical scanning device which enables uniform scan line pitch and high precision image, includes a light source (1) having plural light emitting members, a rotary polygonal mirror (5) having a deflecting surface, a first optical system (LA) for imaging a light beam on the deflecting surface and a second optical system (6) for imaging the light beam on a scan surface (7) to be scanned, wherein the optical axis of the first optical system is disposed at a particular angle in a sub-scan section with respect to a plane perpendicular to the deflection axis of the deflecting surface, and wherein, with respect to the imaging magnification in the sub-scan section of the second optical system on the optical axis and between the deflecting surface and the scan surface, the imaging magnification at a scan start side is made large while the imaging magnification at the scan end side is made small or, alternatively, the imaging magnification at a scan start side is made small while the imaging magnification at the scan end side is made large.