To diagonally cut a pipe and provide a good cut surface without damaging a device.

A cut shape of a pipe 1 is constituted by a cut surface S1 tilted from one side of a peripheral part of the pipe 1 to a right end side in an axial direction, R-shaped cut surface continued to the cut surface S1 to be swollen in a right end side in an axial direction, cut surface S3 continued to the cut surface S2 to be diagonally extended crossing with an axial line in a left end side in an axial line, R-shaped cut surface S4 continued to the cut surface S3 to be swollen in a left end side in an axial direction, and a cut surface S5 continued to the cut surface S4 to be tilted in a right end side in an axial direction to lead to the other side in the peripheral part in a position separated by a prescribed distance to a left end side in an axial direction from the cut surface S1. So as to place partly the cut surface S1, S5, cut surface S2, S3, S4 flush with an opposed surface part T of a fixed/movable core metal 10, 11, a cutting edge of a fixed edge part 5, cutting edge of a movable edge part 7 and a shape of the opposed surface part T are set.