In an optical scanning device of opposite scanning type, two target surfaces for scanning are scanned in opposite main scanning directions by using a single optical deflector. End portions of a scanning lens arranged in a scanning optical system are configured not to have refractive power in the main scanning direction. A synchronization light beam passes through the end portions of the scanning lens and falls on a light receiving element via a synchronizing optical system. The synchronizing optical system includes a first synchronizing lens, a synchronizing fold mirror, and a second synchronizing lens. The synchronizing fold mirror and the light receiving element are arranged to be in a conjugate relation with the second synchronizing lens.