A line beam is irradiated such that edge lines of the beam extend in a direction at an angle of 45.degree. with respect to the vertical direction or the horizontal direction. As a result, a laser defective crystallization region R' where the grain size has not become sufficiently large due to unevenness in intensity of the line beam passes at 45.degree. across the carrier path connecting source and drain regions S and D to each other. The defective crystallization region R' thus does not completely divide between the contact region CT, i.e., the carrier path between the source and drain regions. Therefore, a carrier path CP can be securely maintained without passing through the defective crystallization region R', so that the ON-current is prevented from being reduced. Deterioration or unevenness in transistor characteristics caused by unevenness in intensity of laser irradiation can thus be prevented.