Laser beams emitted by a plurality of laser sources are divided into a plurality of sub-beams, which are irradiated onto selected portions of an amorphous semiconductor on a substrate to crystallize the amorphous semiconductor. A difference in diverging angles between the laser beams is corrected by a beam expander. The apparatus includes a sub-beam selective irradiating system including a sub-beam dividing assembly and a sub-beam focussing assembly. Also, the apparatus includes laser sources, a focussing optical system, and a combining optical system. A stage for supporting a substrate includes a plurality of first stage members, a second stage member disposed above the first stage members, and a third stage member 38C, rotatably disposed above the second stage to support an amorphous semiconductor.