To solve the problem that carrier mobility and an on-state current have been lowered owing to small crystal grains at random in the polysilicon island of a thin-film transistor.

An amorphous silicon layer 3 is formed onto a glass substrate 1 through a substrate cover layer 2. The amorphous silicon layer 3 is irradiated with laser line beams, and polysilicon is grown from the section of the amorphous silicon layer corresponding to the end of laser line beams to the section of the amorphous silicon layer corresponding to the center of laser line beams, thus obtaining a polysilicon layer 3' in which crystal grains are elongated in the cross direction of laser line beams. The polysilicon layer 3' is patterned to the polysilicon island of the thin-film transistor.