A thin film vacuum evaporation device having a reaction gas supplier for locally supplying a reaction gas to the evaporating point on a target. The device includes a reaction chamber that can be kept under vacuum with a light transmitting window disposed therein allowing the passage of a laser beam on the target. Also, a differential pressure chamber may be provided between the target and the light transmitting window, and a gas introducing section may be connected to the differential pressure chamber. Thus, the vapor generated by the target is prevented from adhering to the light transmitting window, and the light transmitting window can be kept clean.