
An optical beam scanning apparatus according to the present invention includes a light source, a pre-deflection optical system, a light deflecting device, a post-deflection optical system, a first sensor configured to detect a part of the luminous fluxes deflected by the light deflecting device, one or plural first optical elements configured to be provided in the post-deflection optical system and act on the luminous fluxes deflected by all the deflection surfaces of the light deflecting device...











