An optical scanning device includes a light source device, a deflector, an input optical system for directing a light beam from the light source device onto the deflector, and an imaging optical system for imaging a light beam scanningly deflected by a deflecting surface of the deflector, upon a scan surface to be scanned, wherein, in a sub-scan section, a light beam directed from the input optical system toward the deflecting surface of the deflector is incident thereon at a finite angle with respect to a plane which is orthogonal to a rotational axis of the deflector, wherein the imaging optical system includes at least one molded imaging lens, and wherein a shape within a sagittal section of at least one lens surface, of lens surfaces of the at least one imaging lens, is non-arcuate, and a sagittal curvature in a light beam passage region has an extreme value.