Scanning optical system in which a ghost image is elminated

A scanning optical system is provided with a deflector for deflecting a light beam, a medium to be scanned by the light beam deflected by the deflector, and an imaging optical system disposed between the medium to be scanned and the deflector. A linear image near the deflecting - reflecting surface of the deflector and a point on the surface of the medium to be scanned are in a conjugate relation through the imaging optical system. The imaging optical system is such that the angle which the optical axis of the imaging optical system forms with respect to the optical axis of the light beam incident on the deflector in a plane parallel to the deflecting plane of the light beam is chosen so that a ghost image is formed in the direction of the scanning line of the medium to be scanned and outside the effective scanning area.