To provide 'a slit processing device of a sheet material' to improve productivity by enabling automatic continuous processing.

This device has a feeding means 1 to feed a sheet foamed material S, a cutting means 12 to slit-process the foamed material S fed by the feeding means 11 in a prescribed shape, an excess part removing means 13 to remove an excess part of the foamed material S after slit-processing and a delivery means 14 to deliver the foamed material S after the excess parts a-d are removed. In this case, the cutting means 12 has a pedestal 22 on which the foamed material S fed by the feeding means 11 is placed, a cutter 23 on which blades 25 to slit-process the foamed material S in a prescribed shape against a plate type support member 24 are vertically provided and arranging an elastic member in a space adjacent to the blades 25 and an air pressure cylinder 26 to move the cutter 23 toward the foamed material on the pedestal 22.