An image reading apparatus including a first image reader for reading the front side of document, and a second image reader configured to read the reverse side of document. The apparatus also includes a storage device to store first image data read by the first image reader and second image data read by the second image reader, and a writing controller for writing the first image data and the second image data in parallel to the storage device. A reading controller then reads the first image data and the second image data sequentially from the storage device, and an image processor processes the first and second image data. An image converter then converts the format of the first image data and/or the second image data to be the same.