An optical apparatus for an image forming apparatus has a laser emission device. The laser emission device has first and second light emission units for emitting first and second laser beams. The first and second laser beams emitted by the light emission units are collimated by a collimator lens, and their radii are regulated by a stop. These laser beams are scanned by a scanning mirror on a photosensitive drum in the main scan direction. Distortion of the scanned first and second laser beams is corrected by first and second f-.theta. lenses. In these f-.theta. lenses, power for focusing the laser beams in the sub-scan direction is larger than power for focusing the laser beam in the main scan direction.