An optical scanning apparatus includes M number of light sources that includes M number of semiconductor lasers and M number of coupling lenses, where M is a positive integer, a deflecting scanning unit that deflects laser beams from the light sources to a surface to be scanned, and a transmission-type prism that deflects optical path of the laser beam from at least one of the light sources by an infinitesimal amount of angle. The prism is disposed between the light sources and the deflecting scanning unit, has an incident surface and an output surface nonparallel to each other, and can rotate around an axis of rotation substantially parallel to the optical path of the laser beam.