In an image reading apparatus for reading a color document as a monochrome image, an image forming apparatus of the invention includes a composite light source that irradiates the color document and includes plural light sources different in spectral distribution, a sensor to detect the intensity of a reflected light from the color document, a light emission ratio setting unit to changeably set light emission ratios different for the respective light sources, and a light source control unit to control effective light amounts of the plural light sources with the set light emission ratios. According to the image forming apparatus of the invention, when the color document is monochromatically read, the reading is performed with the brightness close to the human visual sensitivity, the user can changeably set color sensitivity, and uneven density can be reduced.