Optical scanning device and image forming apparatus

An optical scanning device comprising:

• a first optical system that includes a coupling lens that couples a plurality of light beams;
• a deflector that includes a deflecting surface for deflecting the light beams having passed through the coupling lens;
• and
• a second optical system that focuses the light beams deflected by the deflector on a to-be-scanned surface, the to-be-scanned surface including a writing area that is scanned with the light beams from a write-start position to a write-end position in a main scanning direction, wherein
• a focal length of the coupling lens with respect to a distance between the deflecting surface and the coupling lens is larger than 1 and smaller than 4, and
• a size of the deflecting surface in the main scanning direction is smaller than a width of a light flux of the light beams in the main scanning direction,
• wherein intensities of the light beams increase from a light beam at a center in the main scanning direction toward a light beam at the write-start position and a light beam at the write-end position.