Optical scanning device and image forming apparatus

An optical scanning device that is configured to scan a plurality of to-be-scanned surfaces with light beams, the optical scanning device comprising:

• a light source that includes a plurality of light emitting units for emitting light beams;
• a deflector that includes a deflecting surface for deflecting the light beams from the light source;
• a plurality of scanning optical systems that each correspond to one of the to-be-scanned surfaces and focus the light beams deflected by the deflector on corresponding one of the to-be-scanned surfaces;
• and
• a monitoring optical system that monitors a quantity of light beams emitted from the light source, wherein
• the light beams enter the deflector from a direction inclined with respect to a normal direction of the deflecting surface at least in a sub-scanning direction, and
• the light emitting units are arranged two-dimensionally, and a distance between two light emitting units at opposite ends in a main scanning direction is smaller than a distance between two light emitting units at opposite ends in the sub-scanning direction.