PURPOSE: To make it possible to smoothly and precisely cut a marginal edge of a sheet by inserting a resilient piece into the rear part of a guide groove so as to support a cutter, and by projecting a part of a cutting blade coming out from the guide groove in substantially parallel with one or the other of the surface of the base section, rearward of a slant section in the moving direction of the base section.

CONSTITUTION: An inclined section 3 is formed in the vicinity of a base section 2 by inclining the outer peripheral edge. A cutter fitting aperture 5 substantially parallel with the base section is formed in the center part of the base section 2, piercing from the one to the other surfaces of the base section, and a resilient pieced 6 projecting at one end side of the aperture and left by cutting is provided in the other end part of the aperture. A cutter 10 is of a structure such that a cutting blade 14 adapted to be extended and retracted from and into the forward end of a cutter body 11 by manipulating a slider 13 is disposed in a cutting blade groove 12 in the body 11. When the cutting blade 14 is pushed out, the forward end of the body 11 slightly swings toward a side surface of the base section which receives the blade 14, and accordingly, the support piece 6 slightly deflects so as to give a restoring force by which the cutting blade 14 lightly contacts one surface of the base section 2.