To provide a method and a device for cutting a sheet material, allowing easy cutting of even a film material likely to elongate, and lengthening the life span of a punch and a die.

Plural rows of web material 12 cut in a feed direction are shear-cut at the rear edge 13 perpendicularly to the feed direction every specified length to form sheet pieces 14, 14 of the same size as each sheet material 16. At least two corner parts 15 of each sheet piece 14 are then deformed to open a clearance 17 between two corners of the adjacent sheet pieces 14, and the corner part 15 with the clearance 17 formed is punched with the punch and die. A long piece 13 of the sheet material 16 is thereby cut by shear-cutting, and only the four corners are punched with the punch and die. As a result, punching length can be shortened, the corner part 15 of even a film material 10 likely to elongate can be easily cut, and the life span of the punch and the like can be considerably lengthened by punching without pressing the punch and die to each other.