A deflector deflects a light beam from a light source. A scanning optical system focuses the light beam deflected by the deflector. An image carrying member is located at a focal position of the light beam and includes a surface that is scanned in a main scanning direction with the light beam focused by the scanning optical system. One pixel of an image is formed by a plurality of light spots having different focal positions in at least a sub-scanning direction. At least one light spot from among the light spots is formed on the surface of the image carrying member at a scan timing different from those of rest of the light spots.