To beautifully and easily cut off and separate an unnecessary part of a casting by providing an edge face similar to the outer shape of a cut section of the casting to upper/lower edges, supporting the casting with a similar edge face of the lower edge, abutting the similar shape edge face of the upper edge on the casting and successively bringing these cutting edge faces into slide contact with the outer shape of the casting to allow them to gnow into the cut portion.

An unnecessary part of a casting is placed on a lower edge 3 pairing with a lower die 2 and the casting is set to the lower die 2. In this state, an upper die 5 and an upper edge 6 pairing therewith are descended and abutted on the unnecessary part of the casting supported by the lower edge 3. Further, when the upper die 5 and the upper edge 6 are descended, the upper/lower edges 6, 3 are respectively gnawed thereinto. At this time, since these edges have a similar edge face, these edges are smoothly gnawed thereinto while being fitted to an outer shape of a cutting section and further, shoulder edges are provided to the edges face of the upper/lower edges 6, 3 to prevent the generation of cutting crack in the cut section.