Disclosed is an evaporation method to form a thin film over a substrate, which is characterized in the use of an evaporation source equipped with a plurality of evaporation cells. The evaporation source has a rectangular shape with a long side and a short side wherein the long side is longer than the short side. At least one of the evaporation source and the substrate is relatively moved during the evaporation, which allows the formation of a thin film having a highly uniform thickness in a short time.