PURPOSE: To punch grip holes in a portable paper bag continuously and lightly.

CONSTITUTION: A paper bag is passed between a rotating punching-blade roll and an anvil roll and grip holes are formed by punching the handles of the paper bag. The edge 5 of a punching blade 2 attached to the punching blade roll constitutes an approximately elliptical curved blade consisting of approximately circular parts 6, 7 at both ends and curved parts 8, 9 connecting both ends of the approximately circular parts 6, 7 together. The edge 5 of the punching blade 2 is sharpened, having an upright vertical plane 10 on the outside of its punching part and a tapered face on the inside of the punching part. The edge 5 of the punching blade 2 has an angle of 20° to 40°. Therefore the edge 5, having no straight part, can punch the holes continuously and has so little biting resistance even when punching holes in thick portions that it can deeply bite into the thick portions, allowing the holes to be punched lightly. The edges of the grip holes are sharply punched, and the chips generated by the punching can be discharged easily from the punching blade.