An image scanning device, an image forming apparatus including the image scanning device, and a method of controlling image quality in the image scanning device are provided. The image scanning device includes a document board on which documents to be scanned are placed, a scanning unit which is installed on a lower portion of the document board to be linearly reciprocated, and comprises a scanner including a light guide for irradiating light to the documents, and light emitting devices that are separated from both ends of the light guide and irradiate light, and an image sensor for receiving the light emitted from the scanning unit, wherein, loss of the light emitted from the light emitting devices is compensated for by increasing intensity of electric current supplied to the light emitting devices as a distance between the light emitting devices and the light guide increases.
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