A laser beam temporally modulated in amplitude by a modulator and shaped into a long and narrow shape by a beam shaper is rotated around the optical axis of an image rotator inserted between the beam shaper and a substrate. Thus, the longitudinal direction of the laser beam having the long and narrow shape is rotated around the optical axis on the substrate. In order to perform annealing in a plurality of directions on the substrate, the laser beam shaped into the long and narrow shape is rotated on the substrate while a stage mounted with the substrate is moved only in two directions, that is, X- and Y-directions.In such a manner, the substrate can be scanned at a high speed with a continuous wave laser beam modulated temporally in amplitude and shaped into a long and narrow shape, without rotating the substrate. Thus, a semiconductor film can be annealed.