To allow the corner of an empty box such as a milk pack to be cut off in a quick and stable manner with a cutter having a holder by providing an offset portion that is bent at a certain angle at one end of a handle and mounting a holder plate which has a certain angle in the center front of the outside of the offset portion.

One end 2 of a handle 1 is bent 140 to 160 degrees to form an offset portion 3. A holder plate 4 is mounted in the center of the outer surface of the offset portion 3. The holder plate 4 has an angle of 90 degrees. In the center of the holder plate 4, a blade 5 is mounted such that it protrudes downward and diagonally when viewed from the top of the offset portion 3. The holder plate 4 is made with an angle of 90 degrees for using it for a square or rectangular cube. To cut off the corner of other polygonal products such as triangles and hexagons, the angle of the holder plate 4 needs to be determined in accordance with the angle of the box to be cut. For actual use, the holder plate 4 is applied to the corner of a milk pack being used up, and the handle 1 is pulled downward. The corner of the milk pack is then precisely cut off by the blade 5 in a longitudinal direction.