To reduce the influence of birefringence and to satisfactorily form a spot shape on a surface to be scanned by making the height of optical element at any arbitrary position in the direction of the meridian line less than thickness at that position in the direction of an optical axis.

Concerning parallel light flux made incident to a cylindrical lens 4, the parallel light flux is emitted while keeping its state as it is inside a main scanning cross section. Besides, inside a sub scanning cross section, that light flux is converged and an image is formed almost as the radiograph of the deflecting plane of an optical deflector 5. Then, the light flux deflected and reflected on the deflecting plane of optical deflector 5 is transmitted through a reflection mirror 8 to a photosensitive drum surface 9 by an fθ lens system 10 and by rotating the deflector 5 in a direction A, image recording is performed while optically scanning the photosensitive drum surface 9 in main scanning direction. In all the optical areas to be used for the main scanning direction of this lens 7, the lens 7 is produced so that the height of lens 7 at any arbitrary position in sub scanning direction can be less than the thickness of lens 7 at that position in the direction of the optical axis.