An object is to provide a technology capable of improving a manufacturing yield of semiconductor devices by preventing scattering of irregular-shaped scraps formed at the time of dicing. To achieve the above object, for dicing lines, by which an irregular-shaped outer periphery may possibly be cut off, among a plurality of dicing lines, formation of the dicing lines starts from an outside of a semiconductor wafer, and after the semiconductor wafer is cut off partway, formation of the dicing lines is ended before reaching the irregular-shaped outer periphery formed on a outer periphery of the semiconductor wafer. For other dicing lines, formation of the dicing lines starts from the outside of the semiconductor wafer, and after the semiconductor wafer is cut off, is ended outside the semiconductor wafer.