A light source provided with a laser element that emits a laser beam emits a laser beam for synchronization control. A synchronization mirror reflects the laser beam so as to allow a light receiving element in the light source to detect the laser beam. The synchronization mirror is provided on f-.theta. lenses opposite to a light deflector, such that the f-.theta. lenses are provided neither on a light beam path that connects the light source and the light deflector nor on a light beam path for synchronization control that connects the light deflector and the synchronization mirror.