An image reading apparatus which is capable of appropriately performing show-through reduction processing and foundation color reduction processing in accordance with an operation for changing the color of a background member to another one having different color that is read along with an original. An image reading unit reads an image of a conveyed original. A background member has a white-colored member and a black-colored member and is disposed in such a manner that it opposed to the image reading unit. A moving unit moves the background member. A CPU determines a degree of image processing to be applied to read image data depending on the color of an opposing portion of the background member, which is opposed to the image reading unit that is reading an original.