An image forming apparatus for forming an image in accordance with light caused to be emitted from a light source, the image forming apparatus comprising: a light source; a digital half-toning unit configured to convert a uniform-pixel-value region formed with pixels having a same pixel value of image data to a parallel-line pattern formed with a plurality of parallel lines, wherein the pixels are arranged in a rectangular array having a first axis and a second axis, the first axis being orthogonal to the second axis, the plurality of parallel lines extending obliquely with respect to the first axis and the second axis, thereby expressing each gray level of the image data as an area percentage; a modulated-signal generating unit configured to generate a modulated signal by modulating the image data, in which each gray level is expressed as an area percentage, with a clock signal; and a light-source driving unit configured to drive the light source according to the modulated signal; characterised by: an edge control unit configured to generate an illuminated-region control signal and a light-intensity control signal, the edge control unit configured to narrow a to-be-illuminated region, the to-be-illuminated region being a region which is to be illuminated by light emitted from the light source, in each of edge neighborhoods of the plurality of lines constituting the parallel-line pattern, and the edge control unit also configured to increase the intensity of the light emitted to the edge neighborhoods to become higher than the intensity of light incident on any other portion. a light source; a digital half-toning unit configured to convert a uniform-pixel-value region formed with pixels having a same pixel value of image data to a parallel-line pattern formed with a plurality of parallel lines, wherein the pixels are arranged in a rectangular array having a first axis and a second axis, the first axis being orthogonal to the second axis, the plurality of parallel lines extending obliquely with respect to the first axis and the second axis, thereby expressing each gray level of the image data as an area percentage; a modulated-signal generating unit configured to generate a modulated signal by modulating the image data, in which each gray level is expressed as an area percentage, with a clock signal; and a light-source driving unit configured to drive the light source according to the modulated signal; characterised by: an edge control unit configured to generate an illuminated-region control signal and a light-intensity control signal, the edge control unit configured to narrow a to-be-illuminated region, the to-be-illuminated region being a region which is to be illuminated by light emitted from the light source, in each of edge neighborhoods of the plurality of lines constituting the parallel-line pattern, and the edge control unit also configured to increase the intensity of the light emitted to the edge neighborhoods to become higher than the intensity of light incident on any other portion. an edge control unit configured to generate an illuminated-region control signal and a light-intensity control signal, the edge control unit configured to narrow a to-be-illuminated region, the to-be-illuminated region being a region which is to be illuminated by light emitted from the light source, in each of edge neighborhoods of the plurality of lines constituting the parallel-line pattern, and the edge control unit also configured to increase the intensity of the light emitted to the edge neighborhoods to become higher than the intensity of light incident on any other portion.