A light scanning device comprising: - a first light source that is adapted to emit a first light beam; - a second light source that is adapted to emit a second light beam; - a polygon mirror including a rotation shaft and a deflection surface, the deflection surface being adapted to ensure entering of the first light beam and the second light beam at an identical timing, the polygon mirror being adapted to reflect the first light beam and the second light beam in order to scan the first light beam and the second light beam on a scanned surface in a main-scanning direction, while rotating around the rotation shaft; - a first incidence optical system that is adapted to cause the first light beam having a first incidence opening angle (θ1) to enter the deflection surface; - a second incidence optical system that is adapted to cause the second light beam having a second incidence opening angle (θ2) to enter the deflection surface, the second incidence opening angle (θ2) being different from the first incidence opening angle (θ1); characterized by - a first scanning lens located between the deflection surface and the scanned surface, the first scanning lens being adapted to form an image of the first light beam on the scanned surface; and - a second scanning lens that is adapted to form an image of the second light beam on the scanned surface, wherein the first scanning lens is arranged on top of the second scanning lens in a sub-scanning direction, and - when at a time point, at which the light beam reflected at the deflection surface passes through a position on an optical axis of a scanning lens (6Y, 6C) in plan view of the polygon mirror along an axial direction of the rotation shaft, a reflection point of a light beam on the deflection surface is a reference point, the second scanning lens is arranged at different positions in a main-scanning direction and in an optical axis direction with respect to the first scanning lens, such that a circle locus is along an offset curved line, the circle locus being a locus of a point corresponding to the reference point by the rotation of the polygon mirror, the offset curved line being the circle locus shifted to a downstream side of the optical axis direction. wherein the first incidence optical system and the first scanning lens are located with respect to the polygon mirror, such that the first light beam is reflected at the reference point located at a specific position, and passes through a position on an optical axis of the first scanning lens, and the second incidence optical system and the second scanning lens are located with respect to the polygon mirror, such that the second light beam is reflected at the reference point differently located from the specific position in a rotation direction of the polygon mirror, and passes through a position on an optical axis of the second scanning lens. - a first light source that is adapted to emit a first light beam; - a second light source that is adapted to emit a second light beam; - a polygon mirror including a rotation shaft and a deflection surface, the deflection surface being adapted to ensure entering of the first light beam and the second light beam at an identical timing, the polygon mirror being adapted to reflect the first light beam and the second light beam in order to scan the first light beam and the second light beam on a scanned surface in a main-scanning direction, while rotating around the rotation shaft; - a first incidence optical system that is adapted to cause the first light beam having a first incidence opening angle (θ1) to enter the deflection surface; - a second incidence optical system that is adapted to cause the second light beam having a second incidence opening angle (θ2) to enter the deflection surface, the second incidence opening angle (θ2) being different from the first incidence opening angle (θ1); - a first scanning lens located between the deflection surface and the scanned surface, the first scanning lens being adapted to form an image of the first light beam on the scanned surface; and - a second scanning lens that is adapted to form an image of the second light beam on the scanned surface, wherein the first scanning lens is arranged on top of the second scanning lens in a sub-scanning direction, and - when at a time point, at which the light beam reflected at the deflection surface passes through a position on an optical axis of a scanning lens (6Y, 6C) in plan view of the polygon mirror along an axial direction of the rotation shaft, a reflection point of a light beam on the deflection surface is a reference point, the second scanning lens is arranged at different positions in a main-scanning direction and in an optical axis direction with respect to the first scanning lens, such that a circle locus is along an offset curved line, the circle locus being a locus of a point corresponding to the reference point by the rotation of the polygon mirror, the offset curved line being the circle locus shifted to a downstream side of the optical axis direction.