An image reading apparatus, including an image sensor configured to receive light and output an image signal in accordance with image data carried in the light, an A/D converter configure to convert the image signal into a digital signal with reference to a reference voltage, and a reference white plate configured to be read so as to generate density data. Also included is a correction device configured to correct the digital signal in accordance with shading data, a reference member configured to define a readable density limit, and a detection device configured to detect a ratio of density of the reference white plate to that of the reference member as density adjustment data. The density is obtained by reading the respective reference member and reference white plate in substantially a same exposure condition. Further included is a control device configured to control the correction device to adjust the digital signal in accordance with the density adjustment data.