An image reading device reads an image of an original mounted on an original mounting base by using an optical scanning unit which is subjected to acceleration drive along the original mounting base until a velocity according to a reading magnification is obtained and then scanned by uniform velocity drive. A stepping motor moves the optical scanning unit. A reading magnification acceptance portion accepts a reading magnification of an image of the original mounted on the original mounting base. A motor drive control portion is used for control a drive electric current of the stepping motor, obliquely increases a set electric current during acceleration drive every velocity that the optical scanning unit reaches by a pulse number according to a reading magnification accepted by the reading magnification acceptance portion, and changes the set electric current value in accordance with the reading magnification so as to provide a characteristic for lowering the set electric current value at the time of shifting to uniform velocity drive. A photoelectric conversion portion converts a quantity of reflected light when the original on the original mounting base is optically scanned by the optical scanning unit moved by the stepping motor into an electrical signal.