An image forming apparatus that forms an electrostatic latent image according to light emitted from a light source (2200a, 2200b, 2200c, 2200d), comprising: a pseudo-halftone processing unit that processes input image data to output image data of first resolution; a resolution converting unit that converts the image data of the first resolution into image data of second resolution that is higher than the first resolution; a modulation-signal generating unit that generates a modulation signal obtained by modulating the image data of the second resolution according to a clock signal; a light-source driving unit that drives the light source (2200a, 2200b, 2200c, 2200d) according to the modulation signal; and an electrostatic-latent-image forming unit that forms, on a latent image carrier (2030a, 2030b, 2030c, 2030d), the electrostatic latent image by light emitted from the light source (2200a, 2200b, 2200c, 2200d) by driving the light source (2200a, 2200b, 2200c, 2200d) according to the modulation signal, characterized in that: the pseudo-halftone processing unit converts a region of pixels having the same pixel value in the input image data into a parallel line pattern that is formed with a plurality of parallel lines oblique relative to a direction of arrangement of pixels to express concentration by an area ratio; the resolution converting unit generates the image data of the second resolution in which each edge of the lines forming the parallel line pattern is smoothed; and the resolution converting unit includes a line-region detecting unit that detects the parallel line pattern; an edge detecting unit that detects an edge region that matches with an edge pattern expressing a stepped-shape of an edge of a line of the first resolution from the parallel line pattern; a resolution increasing unit that converts image data of the first resolution into image data of the second resolution to increase resolution; and a smoothing unit that arranges, in a region corresponding to the edge region in the image data of the second resolution, a smooth pattern of the second resolution expressing a shape that is obtained by smoothing the stepped-shape. a pseudo-halftone processing unit that processes input image data to output image data of first resolution; a resolution converting unit that converts the image data of the first resolution into image data of second resolution that is higher than the first resolution; a modulation-signal generating unit that generates a modulation signal obtained by modulating the image data of the second resolution according to a clock signal; a light-source driving unit that drives the light source (2200a, 2200b, 2200c, 2200d) according to the modulation signal; and an electrostatic-latent-image forming unit that forms, on a latent image carrier (2030a, 2030b, 2030c, 2030d), the electrostatic latent image by light emitted from the light source (2200a, 2200b, 2200c, 2200d) by driving the light source (2200a, 2200b, 2200c, 2200d) according to the modulation signal, characterized in that: the pseudo-halftone processing unit converts a region of pixels having the same pixel value in the input image data into a parallel line pattern that is formed with a plurality of parallel lines oblique relative to a direction of arrangement of pixels to express concentration by an area ratio; the resolution converting unit generates the image data of the second resolution in which each edge of the lines forming the parallel line pattern is smoothed; and the resolution converting unit includes a line-region detecting unit that detects the parallel line pattern; an edge detecting unit that detects an edge region that matches with an edge pattern expressing a stepped-shape of an edge of a line of the first resolution from the parallel line pattern; a resolution increasing unit that converts image data of the first resolution into image data of the second resolution to increase resolution; and a smoothing unit that arranges, in a region corresponding to the edge region in the image data of the second resolution, a smooth pattern of the second resolution expressing a shape that is obtained by smoothing the stepped-shape. a line-region detecting unit that detects the parallel line pattern; an edge detecting unit that detects an edge region that matches with an edge pattern expressing a stepped-shape of an edge of a line of the first resolution from the parallel line pattern; a resolution increasing unit that converts image data of the first resolution into image data of the second resolution to increase resolution; and a smoothing unit that arranges, in a region corresponding to the edge region in the image data of the second resolution, a smooth pattern of the second resolution expressing a shape that is obtained by smoothing the stepped-shape.