It is intended to improve work efficiency by eliminating the work of attaching and removing push rods during installing and dismounting the a blade mount and also to reduce abrasion of the push rods for pushing punching scrap out of a punching blade. The first push rods 18 are inserted movably in the first through-holes 16 formed in the knife cylinder and the second push rods 36 are inserted movably in the second through-holes 34 formed in the blade mount to permit the second push rods 36 to be abutted on the first push rods 18. A scrap push lever 30 is mounted on the outer end of the second push rod 36 to push out the punching scrap a and an eccentric cylinder 14 is provided inside of the knife cylinder 10 to push the first push rod 18 outward when pushing out the punching scrap a. The stroke of the first push rod 18 is controlled so that the outer end 18a of the first push rod 18 does not project from the outer periphery 10a of the knife cylinder. The first push rod 18 and the second push rod 36 are preferably made from one of self-lubricating resin and abrasion-resistant material.