Scanning optical device and image forming apparatus

A scanning optical device comprising:

• a first optical system for guiding at least two light beams emitted from at least two light emitting points to deflection means;
• and
• a second optical system for imaging as light spots the at least two light beams deflected by the deflection means on a surface to be scanned,
• wherein the light beams incident to a deflection surface of the deflection means are set to light beams wider than the deflection surface in a main scanning direction and,
• in a main scanning section, when respective angles formed between the center axis of emitted distributions of the light beams from the at least two light emitting points and a corresponding optical axis of the first optical system are each given by αi, the angles among αi with respect to two light beams located at the longest distance from the optical axis are given by α1 and α2, a maximum difference formed between the angles of α1 is given by αε, respective total angular widths of radiation angles of the light beams from the at least two light emitting points within the main scanning section are given by θi, two beam radiation angles in which a difference of the total angular widths is maximum are given by θ1 and θ2, and a difference of the beam radiation angles is given by θε=|θ1−θ2|,
• 2≧|α1−α2|≧0 4≧|α1+α2|≧0, and 2÷αε/(1+θε)≧0
• are satisfied, where θi is a range up to 1/e2 of a peak of an intensity distribution of each of the light beams.