An object is to provide a laser irradiation apparatus and a laser irradiation method with which positions of crystal grain boundaries generated at the time of laser crystallization can be controlled. Laser light emitted from a laser 101 is modulated into laser light having intensity distribution along a long-axis direction through a phase shift mask 103 and is transferred to an amorphous semiconductor film provided over an insulating substrate by a cylindrical lens 104 and a lens 105. The amorphous semiconductor film is crystallized by being scanned with the laser light.