An optical scanning device includes a light source, a deflector, and a plurality of scanning lenses. A scanning lens lying closest to the deflector has a positive refractive power and the incident surface of it allows the oblique angle θ of the light beam entering the incident surface to vary from a center to an end of the incident surface. The incident surface satisfies the following conditions, where Δθ is the amount of change and dθ is the rate of change in the oblique angle θ of the light beam in the main scanning direction, d2θ is the rate of change in dθ, and Δ2θ is the amount of change in Δθ: d2θ