An image reading apparatus that reads an image. Image data generated by a scanner reading an original is stored in a RAM. The size of the image data and the size of a region for storing the image data in the RAM are compared with each other. The image data is divided when the size of the image data is larger than the size of the region for storing the image data in the RAM. One of a plurality of pieces of image data divided from the image data is stored in the RAM, and the format of the image data stored in the RAM is converted. One image file including image data obtained by converting each piece of the plurality of pieces of image data is generated.