There is disclosed an electrophotographic printer for projecting light from light source emitted according to image data onto a photoconductive body performing a mechanical scan operation in a subscan direction so as to form an image of the image data thereon, and for printing the image on a piece of printing paper using the electrophotographic process. In the electrophotographic printer, the light source comprises plural light emitting devices such as LEDs aligned in a main scan direction perpendicular to the subscan direction, and each light emitting device has a light output opening elongated in the subscan direction. Image data received from an external unit are once stored in an image memory, and the image data read therefrom are Fourier transformed. Thereafter, the Fourier transformed data are multiplied by a predetermined frequency characteristic defined by the shape of each light output opening, and data of the obtained product are Fourier inverse transformed as the image data to be printed, thereby improving a deterioration of the quality of said printed image caused when said light output opening is used.