PURPOSE: To prevent the accident of injury caused by a cutting blade by providing a guide plate, to which a deformable safety holding spring is attached, and a handle and holding the edge of the cutting blade in the same direction as the long axis of the handle to minimize the non-uniform pulling, bending and entangling of a blade.

CONSTITUTION: An edge cutter apparatus 10 is provided with a pair of guide plates 12 and 14 mutually opened just at an obtuse angle , and this obtuse angle is set to 93°. Besides, on the guide plates 12 and 14, planar surfaces 12A and 14A are formed so as to be abutted with edge parts at the edges of a side wall panel linked along with the corner line of a box. The respective guide plates are respectively equipped with leading edges 12E and 14E so that the cutter apparatus can be moved on a rugged surface. A blade 20 provided with a cutting blade edge 20E is clamped between blade holding plates 16 and 18 by a fastener 22. A handle is extended while being inclined just at an acute angle θ with respect to the planar surface 12A of the guide plate, and a protecting spring 30 is equipped with a bent arm part 30A extended from a rugged connecting part 32 on the guide plate 12 and protruded from a window 34 formed on the guide plate 12.