Deflection of multiple laser beams, scanning of the photoreceptors by such beams in the main scanning direction and light path separation in the sub scanning direction are carried out by having multiple laser beams strike the same deflecting reflective surface of the deflector at different angles in the sub scanning direction. In order to adjust the incident angles in the sub scanning direction, the angles of the laser beams are simultaneously changed. In order to adjust the incident positions in the sub scanning direction, the laser beams are simultaneously moved in a parallel fashion by a light source adjustment unit.