An image reading device for reading an image on a document with visible light and non-visible light being switchingly applied thereto, comprising: an image sensor which reads the image on the document to output an image signal and whose sensitivity of non-visible light is lower than sensitivity of visible light; a light source which switchingly emits visible light and non-visible light when reading the image on the document; lighting control means for controlling lighting periods of the light source, wherein the lighting control means is adapted to perform control such that a first light source lighting period for applying non-visible light is longer than a second light source lighting period for applying visible light so as to equalize the levels of the image data upon application of visible light and non-visible light before the image sensor starts to read the image on the document; and an adjusting unit which fine-tunes the first and second light source lighting periods on the basis of a pre-set first reference level as a reference for extending or shortening the first light source lighting period and a pre-set second reference level as a reference for extending or shortening the second light source lighting period, respectively, in the reading operation, wherein the adjusting unit compares a first image signal level when non-visible light is emitted with said pre-set first reference level, to extend the first light source lighting period when the first image signal level is less than said pre-set first reference level and to shorten the first light source lighting period when the first image signal level is greater than said pre-set first reference level, and compares a second image signal level when visible light is emitted with said pre-set second reference level, to extend the second light source lighting period when the second image signal level is less than the second reference level and to shorten the second light source lighting period when the second image signal level is greater than said pre-set second reference level. an image sensor which reads the image on the document to output an image signal and whose sensitivity of non-visible light is lower than sensitivity of visible light; a light source which switchingly emits visible light and non-visible light when reading the image on the document; lighting control means for controlling lighting periods of the light source, wherein the lighting control means is adapted to perform control such that a first light source lighting period for applying non-visible light is longer than a second light source lighting period for applying visible light so as to equalize the levels of the image data upon application of visible light and non-visible light before the image sensor starts to read the image on the document; and an adjusting unit which fine-tunes the first and second light source lighting periods on the basis of a pre-set first reference level as a reference for extending or shortening the first light source lighting period and a pre-set second reference level as a reference for extending or shortening the second light source lighting period, respectively, in the reading operation, wherein