An image reading apparatus includes a first reading part which reads a first side of a document, a second reading part located on a document discharge path which reads a second side of the document with an image sensor, a path narrowing member positioned across from the image sensor on the document discharge path; and an adjusting unit, wherein the adjusting unit adjustably moves the path narrowing member closer to and farther away from the image sensor in order to correspondingly move the document closer to and farther away from the image sensor. The image reading apparatus is capable of increasing reading speed when a one-side reading of a document is performed as well as minimizing any damage done to data produced by the reading when a double-side reading of a document is performed. Thus, the present invention is capable of increasing a reading speed when an one-side reading is performed as well as minimizing any damages done to data produced by the reading when a double-side reading is performed, and an image forming apparatus including the same.