An optical scanning device has a light shield plate where a scanning line emitted from a light source passes through a scanning lens, and is reflected by a rotation polygon mirror, and after that, passes through the scanning lens again, and is reflected by the scanning lens at the opposite side of the rotation polygon mirror by nipping the scanning lens, wherein the light shield plate is placed at a position wherein the distance between the rotation polygon mirror and the scanning lens, the thickness in the optical axial direction of the scanning lens, the angle by which the scanning line incident the rotation polygon mirror and the convergent angle of the scanning line satisfies a certain relationship.