PURPOSE: To provide a knock-out punching too, which can form a knock-out hole easily and securely without generating the crack at the time of forming a knock-out hole in the side wall of a box or the like.

CONSTITUTION: This knock-out hole punching tool 10 has the structure like a cutting pliers and provided with two shanks 18, 19 crossing each other. The tip of one of the shanks 18, 19 is provided with a support part made of a support body 11, which is formed into a circular-shape in response to the shape of a circular knock-out 22, and the tip of the other shank is provided with a punching part made of a prism-shape punching body 12. The shanks 18, 19 of the knock-out hole punching toll 10 are gripped to lower the punching body 12 to the center of the support body 11 and project the tip of the punching body 12 to the opposite side to punch the knock-out 22.