A laser beam scanner (53) is provided to project a laser beam onto the surface of an electrically charged image carrier (5). The laser scanner (53) has a semiconductor laser array (21) equipped with a plurality of light-emitting portions (21a) and a rotary polygonal mirror (3) that deflects the laser beam from the light-emitting portions (21a) toward the image carrier (5). The light-emitting portions (21a) are two-dimensionally arranged on the surface of the semiconductor laser array. The light-emitting portions (21a) are individually controlled for their turn-on and quantity of light by a controller (60). There is thus provided a high-speed and high-resolution laser beam scanner that has a low scanning frequency and a short optical path.