An image reading-out apparatus including a background level detecting circuit, an analog-to-digital converter, and a black-shading compensation circuit. The background level detecting circuit is configured to detect the background level of the original document from the image data. The analog-to-digital converter is configured to remove an influence due to the color of the background on the original document from the image data and configured to perform the analog-to-digital conversion of the image data in accordance with the detected background level. The black-shading compensation circuit is configured to perform black-shading compensation of the image data after the analog-to-digital conversion. The black-shading compensation circuit includes plural black level values calculating circuits which are configured to respectively obtain, per each one line, black level values employed for the black-shading compensation from the image data by use of respective different calculation members; a selection circuit which is configured to select and output one black level value among plural sorts of the black level values outputted by the plural black level values calculating circuits; and a subtracter which is configured to subtract the selected black level value from the image data after performing the analog-to-digital conversion and the black-shading compensation.