1.  Field of the Invention
The present invention relates to an optical beam scanning device that causes a light beam from a light source to scan in a main scanning direction on photoconductive surfaces of photoconductive members, and, more particularly to a technique for realizing improvement of an optical characteristic. 
2.  Description of the Related Art
Conventionally, there is known a technique for, in image forming apparatuses that perform image formation of electrostatic latent images and the like on photoconductive members according to irradiation of light beams, setting plural reflecting surfaces in a rotating deflector, which performs scanning of light beams on plural photoconductive members, to have different tilt angles with respect to a rotation axis and causing the light beams to perform scanning of different photoconductive members for each of the reflecting surfaces having the different tilt angles (see JP-A-2000-2846 and JP-A-11-218991). 
In a pre-deflection optical system in the conventional technique, a ray is made incident from the outside of a scanning range of a post-deflection optical system.  In the conventional optical beam scanning device having such as constitution, there is a problem in that, when it is attempted to adopt an overfilled optical system advantageous for an increase in speed, it is difficult to keep main scanning direction beam diameters (which affect uniformity of quantities of light) uniform and an optical characteristic is not stabilized.