PURPOSE: To ensure that a minimum transport distance is used for transport constantly and thereby cutting capability is improved, even if the cutting angle of a strap material is changed by setting a gyrating center of the strap material at a crossing point among the tip of a strap material of maximum width with a minimum cutting angle, the tip of a strap material with a maximum cutting angle and a cutting line of a strap material.

CONSTITUTION: When a strap material 1a with a minimum cutting angle αat a width W and a strap material 1b with a maximum cutting angle β at the width W are cut along a cutting line X-X using a cutting device, the gyrating center of the strap materials 1a, 1b are set at a crossing point Q among the tip of the strap material 1a with a maximum width W at a minimum angle α, the tip Pa of the strap material 1b at a maxims angle β and the cutting line X-X of the strap materials 1a, 1b. Subsequently, even if the cutting angles α, β of the strap materials 1a, 1b are changed, the strap material can be transported constantly using a minimum transport distance A. As a result, it is possible to enhance the cutting capability of a cutting device significantly.