A display device is manufactured by forming a semiconductor film over a substrate and irradiating the film with laser light. The laser light is generated from an oscillator, passes through an attenuator that includes a filter, and passes through an optical system after passing through the attenuator. A first region of the semiconductor film is irradiated with the laser light passed through the optical system such that one point of the first region of the semiconductor film is irradiated with at least two shots. A second region of the semiconductor film is also irradiated with the laser light passed through the optical system such that one point of the second region of the semiconductor film is irradiated with at least two shots. The first region and the second region have a portion at which they overlap, and the semiconductor film is etched into semiconductor layers for transistors in areas outside the portion.